Magnetic tape and magnetic tape device

ABSTRACT

The magnetic tape includes a magnetic layer having ferromagnetic powder and a binder on a non-magnetic support, in which the magnetic layer includes a timing-based servo pattern, the ferromagnetic powder is ferromagnetic hexagonal ferrite powder having an activation volume equal to or smaller than 1,600 nm3, and an edge shape of the timing-based servo pattern specified by a magnetic force microscope observation is a shape in which a difference (l99.9−l0.1) between a value l99.9 of a cumulative frequency function of 99.9% of a position deviation width from an ideal shape in a longitudinal direction of the magnetic tape and a value l0.1 of the cumulative frequency function of 0.1% thereof is equal to or smaller than 180 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2016-117339 filed on Jun. 13, 2016. The aboveapplication is hereby expressly incorporated by reference, in itsentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape and a magnetic tapedevice.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes (hereinafter, also simplyreferred to as “tapes”) are mainly used for data storage such as databack-up or archive. The recording of information into magnetic tape isnormally performed by recording a magnetic signal on a data band of themagnetic tape. Accordingly, data tracks are formed in the data band.

An increase in recording capacity (high capacity) of the magnetic tapeis required in accordance with a great increase in information contentin recent years. As means for realizing high capacity, a technology ofdisposing the larger amount of data tracks in a width direction of themagnetic tape by narrowing the width of the data track to increaserecording density is used.

However, when the width of the data track is narrowed and the recordingand/or reproduction of magnetic signals is performed by allowing therunning of the magnetic tape in a magnetic tape device (normallyreferred to as a “drive”), it is difficult that a magnetic head properlyfollows the data tracks in accordance with the position change of themagnetic tape in the width direction, and errors may easily occur at thetime of recording and/or reproduction. Thus, as means for preventingoccurrence of such errors, a system using a head tracking servo using aservo signal (hereinafter, referred to as a “servo system”) has beenrecently proposed and practically used (for example, see U.S. Pat. No.5,689,384A).

SUMMARY OF THE INVENTION

In a magnetic servo type servo system among the servo systems, a servosignal (servo pattern) is formed in a magnetic layer of a magnetic tape,and this servo pattern is magnetically read to perform head tracking.More specific description is as follows.

First, a servo head reads a servo signal formed in a magnetic layer. Aposition of a magnetic head of the magnetic tape in a width direction iscontrolled in accordance with the read servo signal. Accordingly, whenrunning the magnetic tape in the magnetic tape device for recordingand/or reproducing a magnetic signal (information), it is possible toincrease an accuracy of the position of the magnetic head following thedata track, even when the position of the magnetic tape is changed inthe width direction with respect to the magnetic head. By doing so, itis possible to properly record information on the magnetic tape and/orproperly reproduce information recorded on the magnetic tape.

As the magnetic servo type servo system described above, a timing-basedservo type is widely used in recent years. In a timing-based servo typeservo system (hereinafter, referred to as a “timing-based servosystem”), a plurality of servo patterns having two or more differentshapes are formed in a magnetic layer, and a position of a servo head isrecognized by an interval of time when the servo head has reproduced(read) the two servo patterns having different shapes and an interval oftime when the two servo patterns having the same shapes are reproduced.The position of the magnetic head of the magnetic tape in the widthdirection is controlled based on the position of the servo headrecognized as described above.

Meanwhile, it is required that recording density is increased(high-density recording is realized) in the magnetic tape, in accordancewith a great increase in information content of recent years. As amethod for achieving high-density recording, a method of decreasing aparticle size of ferromagnetic powder included in a magnetic layer(hereinafter, referred to as “micronization”) and increasing a fillingpercentage of the ferromagnetic powder of the magnetic layer is used. Inregards to this point, as the ferromagnetic powder for satisfying bothmicronization and excellent magnetic properties, ferromagnetic hexagonalferrite powder among various ferromagnetic powder forms is suitable. Inaddition, as an index of a particle size of the ferromagnetic powder, anactivation volume which is a unit of magnetization reversal can be used.

With such a point, the inventors have examined a technology of applyinga magnetic tape including ferromagnetic hexagonal ferrite powder havinga small activation volume as ferromagnetic powder in a magnetic layer toa timing-based servo system. However, in the intensive studies of theinventors, it was clear that, a phenomenon which was not known in therelated art occurred, in which an accuracy of the position of a magnetichead following a data track in a timing-based servo system (hereinafter,referred to as a “head positioning accuracy”) is decreased in a magnetictape including ferromagnetic hexagonal ferrite powder having anactivation volume equal to or smaller than 1,600 nm³ in a magneticlayer.

Therefore, an object of the invention is to improve a head positioningaccuracy of a timing-based servo system in a magnetic tape includingferromagnetic hexagonal ferrite powder having an activation volume equalto or smaller than 1,600 nm³ in a magnetic layer.

According to one aspect of the invention, there is provided a magnetictape comprising: a magnetic layer including ferromagnetic powder and abinder on a non-magnetic support, in which the magnetic layer includes atiming-based servo pattern, the ferromagnetic powder is ferromagnetichexagonal ferrite powder having an activation volume equal to or smallerthan 1,600 nm³, and an edge shape of the timing-based servo patternspecified by a magnetic force microscope observation is a shape in whicha difference (l_(99.9)−l_(0.1)) between a value l_(99.9) of a cumulativefrequency function of 99.9% of a position deviation width from an idealshape in a longitudinal direction of the magnetic tape and a valuel_(0.1) of the cumulative frequency function of 0.1% thereof(hereinafter, also simply referred to as a “difference(l_(99.9)−l_(0.1))”) is equal to or smaller than 180 nm. In thespecification, the longitudinal direction of the magnetic tape may besimply referred to as a longitudinal direction, and the width directionof the magnetic tape may be referred to as a tape width direction orsimply a width direction. The “width direction” of the invention and thespecification means a direction orthogonal to the longitudinaldirection. In addition, in the invention and the specification, theferromagnetic hexagonal ferrite powder means an aggregate of a pluralityof ferromagnetic hexagonal ferrite particles. Hereinafter, particles(ferromagnetic hexagonal ferrite particles) configuring theferromagnetic hexagonal ferrite powder are also referred to as“hexagonal ferrite particles” or simply “particles”. The aggregate notonly includes an aspect in which particles configuring the aggregatedirectly come into contact with each other, but also includes an aspectin which a binder, an additive, or the like is interposed between theparticles. The points described above are also applied to various powderforms of the invention and the specification such as non-magneticpowder, in the same manner.

The “activation volume” is a unit of magnetization reversal. Regardingthe activation volume described in the invention and the specification,magnetic field sweep rates of a coercivity He measurement part at timepoints of 3 minutes and 30 minutes are measured by using an oscillationsample type magnetic-flux meter, and the activation volume is a valueacquired from the following relational expression of He and anactivation volume V.Hc=2Ku/Ms{(1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant, Ms: saturationmagnetization, k: Boltzmann's constant, T: absolute temperature, V:activation volume, A: spin precession frequency, and t: magnetic fieldreversal time]

The “timing-based servo pattern” of the invention and the specificationis a servo pattern with which the head tracking of the timing-basedservo system can be performed. The timing-based servo system is asdescribed above. The servo pattern with which the head tracking of thetiming-based servo system can be performed, is formed in the magneticlayer by a servo pattern recording head (also referred to as a “servowrite head”) as a plurality of servo patterns having two or moredifferent shapes. As an example, the plurality of servo patterns havingtwo or more different shapes are continuously disposed at regularintervals for each of the plurality of servo patterns having the sameshapes. As another example, different types of the servo patterns arealternately disposed. In regards to the servo patterns having the sameshapes, positional deviations of edge shapes of the servo patterns maybe ignored. The shapes of the servo pattern with which the head trackingof the timing-based servo system can be performed and the dispositionthereof on a servo band are well known and specific aspect thereof willbe described later. Hereinafter, the timing-based servo pattern is alsosimply referred to as a servo pattern. In the invention and thespecification, the edge shape of the timing-based servo patternspecified by magnetic force microscope observation is a shape of an edge(end side) positioned on a downstream side with respect to a magnetictape running direction (hereinafter, also simply referred to as a“running direction”) when recording a magnetic signal (information). Inthe specification, as heads, a “servo write head”, a “servo head”, and a“magnetic head” are disclosed. The servo write head is a head whichperforms recording of a servo signal as described above. (that is,formation of a servo pattern). The servo head is a head which performsreproduction of the servo signal (that is, reading of the servopattern), and the magnetic head is a head which performs recordingand/or reproduction of information, unless otherwise noted.

Next, the edge shape of the timing-based servo pattern specified bymagnetic force microscope observation, a difference (l_(99.9)−l_(0.1))between a value l_(99.9) of a cumulative frequency function of 99.9% ofa position deviation width from an ideal shape of the edge shape in alongitudinal direction of the magnetic tape and a value l_(0.1) of thecumulative frequency function of 0.1% thereof, and the ideal shape ofthe invention and the specification will be described.

Hereinafter, a linear servo pattern which continuously extends from oneside to the other side in a width direction of the magnetic tape and istilted by an angle α with respect to the width direction of the magnetictape will be mainly described as an example. The angle α is an angleformed by a line segment connecting two portions of end portions of theedge of the servo pattern positioned on a downstream side with respectto a magnetic tape running direction when recording a magnetic signal(information), in the tape width direction, and the width direction ofthe magnetic tape. Details are described as follows including thispoint.

In a magnetic tape used in a linear recording system which is widelyused as a recording system of the magnetic tape device, for example, aplurality of regions (referred to as “servo bands”) where servo patternsare formed are normally present in the magnetic layer along alongitudinal direction of the magnetic tape. A region interposed betweentwo servo bands is referred to as a data band. The recording ofinformation (magnetic signals) is performed on the data band and aplurality of data tracks are formed in each data band along thelongitudinal direction. FIG. 1 shows an example of disposition of databands and servo bands. In FIG. 1, a plurality of servo bands 10 aredisposed to be interposed between guide bands 12 in a magnetic layer ofa magnetic tape 1. A plurality of regions 11 each of which is interposedbetween two servo bands are data bands. The servo pattern is amagnetized region and is formed by magnetizing a specific region of themagnetic layer by a servo write head. The region magnetized by the servowrite head (position where a servo pattern is formed) is determined bystandards. For example, in a LTO Ultrium format tape which is based on alocal standard, a plurality of servo patterns tilted in a tape widthdirection as shown in FIG. 2 are formed on a servo band whenmanufacturing a magnetic tape. Specifically, in FIG. 2, a servo frame SFon the servo band 10 is configured with a servo sub-frame 1 (SSF1) and aservo sub-frame 2 (SSF2). The servo sub-frame 1 is configured with an Aburst (in FIG. 2, reference numeral A) and a B burst (in FIG. 2,reference numeral B). The A burst is configured with servo patterns A1to A5 and the B burst is configured with servo patterns BI to B5.Meanwhile, the servo sub-frame 2 is configured with a C burst (in FIG.2, reference numeral C) and a D burst (in FIG. 2, reference numeral D).The C burst is configured with servo patterns C1 to C4 and the D burstis configured with servo patterns D1 to D4. Such 18 servo patterns aredisposed in the sub-frames in the arrangement of 5, 5, 4, 4, as the setsof 5 servo patterns and 4 servo patterns, and are used for recognizingthe servo frames. FIG. 2 shows one servo frame, but a plurality of servoframes are disposed in each servo band in a running direction. In FIG.2, an arrow shows the running direction.

FIG. 3 and FIG. 4 are explanatory diagrams of the angle α. Regarding theservo patterns tilted towards an upstream side of the running directionsuch as the servo patterns A1 to A5 and C1 to C4 in the servo patternsshown in FIG. 2, an angle formed by a line segment (broken line L1 inFIG. 3) connecting two portions of end portions of an edge E_(L) on thedownstream side and a tape width direction (broken line L2 in FIG. 3) isset as the angle α. Meanwhile, regarding the servo patterns tiltedtowards a downstream side of the running direction such as the servopatterns B1 to B5 and D1 to D4, an angle formed by a line segment(broken line L1 in FIG. 4) connecting two portions of end portions of anedge E_(L) on the downstream side and a tape width direction (brokenline L2 in FIG. 4) is set as the angle α. This angle α is normallycalled an azimuth angle and is determined by setting a servo write headwhen forming a magnetized region (servo pattern) on a servo band.

When the servo pattern is ideally formed when forming a magnetizedregion (servo pattern) on a servo band, the edge shape of the servopattern tilted by the angle α with respect to the magnetic tape widthdirection is identical to the shape of the line segment (broken line L1in FIGS. 3 and 4) connecting two portions of end portions of the edge.That is, the edge shape is a shape of a linear line. Accordingly, ineach portion on the edge, a position deviation width from the idealshape in the longitudinal direction of the magnetic tape (hereinafter,also simply referred to as a “position deviation width”) becomes zero.However, in the intensive studies of the inventors, the inventors haveconsidered that, in the magnetic tape including ferromagnetic hexagonalferrite powder having an activation volume equal to or smaller than1,600 nm³ in a magnetic layer as ferromagnetic powder, as shown in FIG.5, a high tendency of a deviation of the edge shape of the servo patternfrom the ideal shape, a great position deviation width, and a greatvariation in values of the position deviation width at each portion ofthe edge may cause a decrease in the head positioning accuracy of thetiming-based servo system. The inventors have surmised that the reasonof the high tendency of the deviation of the edge shape of the servopattern from the ideal shape, in the magnetic tape includingferromagnetic hexagonal ferrite powder having an activation volume equalto or smaller than 1,600 nm³ in a magnetic layer as ferromagneticpowder, is because the arrangement of particles of the ferromagnetichexagonal ferrite powder of the magnetic layer is easily disordered dueto a small activation volume which is equal to or smaller than 1,600nm³, and thus, a magnetic strain may easily occur. However, this ismerely a surmise. In regards to this point, it is considered that thecapacity of the servo write head is increased, specifically, a servowrite head having a great magnetic field (leakage field) is used, inorder to prevent a deviation of the edge shape of the servo pattern fromthe ideal shape. However, even with the intensive studies of theinventors, it was clear that there is a limit for the edge shape of theservo pattern to be close to the ideal shape, in the magnetic tapeincluding ferromagnetic hexagonal ferrite powder having an activationvolume equal to or smaller than 1,600 nm³ in a magnetic layer asferromagnetic powder, only by increasing the capacity of the servo writehead. Therefore, the inventors have thought that the edge shape of theservo pattern should be close to the ideal shape according to theperformance of the magnetic tape in which the servo pattern is formed,and have made a further intensive research regarding the performance ofthe magnetic tape. As a result, the inventors have newly found that aservo pattern having an edge shape close to an ideal shape can be formedin the magnetic tape including ferromagnetic hexagonal ferrite powderhaving an activation volume equal to or smaller than 1,600 nm³ in amagnetic layer as ferromagnetic powder, and accordingly, improvement ofthe head positioning accuracy of the timing-based servo system can beachieved, and have completed the invention regarding the magnetic tape.

The difference (l_(99.9)−l_(0.1)) is a value which can be an indexindicating that the position deviation width from the ideal shape ateach position of the edge of the servo pattern is small and a variationin values of the position deviation width at each portion of the edge issmall. The difference (l_(99.9)−l_(0.1)) is a value acquired by thefollowing method.

A surface of the magnetic layer of the magnetic tape in which the servopattern is formed is observed with a magnetic force microscope (MFM). Ameasurement range is set as a range including five servo patterns. Forexample, in a LTO Ultrium format tape, five servo patterns of the Aburst or B burst can be observed by setting the measurement range as arange of 90 μm×90 μm. The servo pattern (magnetized region) is extractedby performing the measurement (rough measurement) regarding themeasurement range at a pitch of 100 nm. In the invention and thespecification, the expression of the surface of the magnetic layer isused as the same meaning of the surface of the magnetic tape on themagnetic layer side.

After that, in order to detect a boundary between a magnetized regionand a non-magnetized region of the servo pattern in the edge positioningon the downstream of the running direction, a magnetic profile isobtained by performing the measurement in the vicinity of the boundaryat a pitch of 5 nm. In a case where the obtained magnetic profile istilted by the angle α with respect to the width direction of themagnetic tape, rotation correction of the magnetic profile is performedso as to be along the magnetic tape width direction (so that α=0°) byanalysis software. After that, a position coordinate of a peak value ofeach profile measured at a pitch of 5 nm is calculated by the analysissoftware. This position coordinate of the peak value shows a position ofa boundary between the magnetized region and the non-magnetized region.The position coordinate is, for example, specified by an xy coordinatesystem in which a running direction is set as an x coordinate and awidth direction is set as a y coordinate.

In a case in which the ideal shape is a shape of a linear line and theposition coordinate of a position on the linear line is (x,y)=(a,b), forexample, when the edge shape (position coordinate of the boundary)actually acquired is identical to the ideal shape, the calculatedposition coordinate becomes (x,y)=(a,b). In this case, the positiondeviation width becomes zero. With respect to this, when the edge shapeactually acquired is deviated from the ideal shape, the x coordinate ofthe position of y=b of the boundary becomes x=a+c or x=a−c. Thecoordinate x=a+c, for example, indicates a case of the edge shapedeviated by a width c on the upstream side of the running direction, andthe coordinate x=a−c, for example, indicates a case of the edge shapedeviated by a width c (that is, when the upstream side is set as thebase, −c) on the downstream side of the running direction. Here, c isthe position deviation width. That is, an absolute value of the positiondeviation width of the x coordinate from the ideal shape is a positiondeviation width from the ideal shape in the longitudinal direction ofthe magnetic tape. By doing so, the position deviation width at eachposition of edge on the downstream side of the running directionacquired by the measurement at a pitch of 5 nm is acquired.

A cumulative frequency function is obtained from the values obtainedregarding each servo pattern by analysis software. The value l_(99.9) ofcumulative frequency function of 99.9% and the value l_(0.1) of thecumulative frequency function of 0.1% are acquired from the obtainedcumulative frequency function, and the difference (l_(99.9)−l_(0.1)) ofeach servo pattern is acquired from the obtained values.

The measurement described above is performed in a measurement range ofthree different portions (measurement number N=3).

An arithmetical mean of the obtained differences (l_(99.9)−l_(0.1)) ofservo patterns is defined as the difference (l_(99.9)−l_(0.1)) regardingthe magnetic tape.

The “ideal shape” of the edge shape of the servo pattern of theinvention and the specification indicates an edge shape in a case wherethe servo pattern is formed without a position deviation. For example,in one aspect, the servo pattern is a linear servo pattern whichcontinuously or discontinuously extends from one side to the other sidein the width direction of the magnetic tape. The “linear shape” of theservo pattern does not include a curved portion as the pattern shape,regardless of the position deviation of the edge shape. The “continuousstate” means that the line does not have an inflection point at a tiltangle, is not broken, and extends from one side to the other side in thetape width direction. An example of the servo pattern which continuouslyextends from one side to the other side in the width direction of themagnetic tape is the servo pattern shown in FIG. 2. In contrast, the“discontinuous state” means that the line has one or more inflectionpoints at a tilt angle and/or extends while being broken at one or moreportions. A shape of the line which has an inflection point at a tiltangle but extends without being broken is a so-called polygonal lineshape. An example of a discontinuous servo pattern which has oneinflection point at a tilt angle and extends from one side to the otherside in the tape width direction without being broken is a servo patternshown in FIG. 6. Meanwhile, an example of a discontinuous servo patternwhich does not have an inflection point at a tilt angle and extends fromone side to the other side in the tape width direction while beingbroken at one portion is a servo pattern shown in FIG. 7. In addition,an example of a discontinuous servo pattern has one inflection point ata tilt angle and extends from one side to the other side in the tapewidth direction while being broken at one portion is a servo patternshown in FIG. 8.

The “ideal shape” of the edge shape of the linear servo pattern whichcontinuously extends from one side to the other side in the tape widthdirection is a shape (linear shape) of a line segment connecting twoportions of end portions of the edge on the downstream side of therunning direction of the linear servo pattern. For example, the linearservo pattern shown in FIG. 2 has a linear shape shown as L1 in FIG. 3or FIG. 4. Meanwhile, the ideal shape of the linear servo pattern whichdiscontinuously extends is a shape (linear shape) of a line segmentconnecting one end to the other end of portions having the same tiltangle regarding a shape having an inflection point of tilt angles. Inaddition, the shape extending while being broken at one or more portionsis a shape (linear shape) of a line segment connecting one end to theother end of each portion which continuously extends. For example, aservo pattern shown in FIG. 6 includes a line segment connecting e1 ande2 to each other and a line segment connecting e2 and e3 to each other.A servo pattern shown in FIG. 7 includes a line segment connecting e4and e5 to each other and a line segment connecting e6 and e7 to eachother. A servo pattern shown in FIG. 8 includes a line segmentconnecting e8 and e9 to each other and a line segment connecting e10 ande11 to each other.

Hereinabove, the linear servo pattern has been described as an example,but the servo pattern may be a servo pattern in which the ideal shape ofthe edge shape is a curved shape.

For example, regarding a servo pattern in which an edge shape on adownstream side with respect to the running direction is ideally apartial arc shape, the difference (l_(99.9)−l_(0.1)) can be acquiredfrom a position deviation width acquired with a position coordinate ofthe edge shape on the downstream side with respect to the runningdirection acquired by using a magnetic force microscope, with respect toa position coordinate of the partial arc.

As the magnetic force microscope used in the measurement describedabove, a commercially available magnetic force microscope or a magneticforce microscope having a well-known configuration can be used in afrequency modulation (FM) mode. As a probe of the magnetic forcemicroscope, for example, SSS-MFMR (nominal radius of curvature of 15 nm)manufactured by Nanoworld can be used. A distance between the surface ofthe magnetic layer and a tip of the probe at the time of the magneticforce microscope observation is in a range of 20 to 50 nm.

In addition, as the analysis software, commercially available analysissoftware or analysis software with a well-known operational expressioncan be used.

In one aspect, the timing-based servo pattern is a linear servo patternwhich continuously extends from one side to the other side in a widthdirection of the magnetic tape and is tilted by an angle α with respectto the width direction, and has the ideal shape which is a linear shapeextending in a direction of the angle α. An example of the aspect is aservo pattern shown in FIG. 2.

In one aspect, a tilt cos θ (hereinafter, also simply referred to as“cos θ”) of the ferromagnetic hexagonal ferrite powder with respect to asurface of the magnetic layer acquired by cross section observationperformed by using a scanning transmission electron microscope in themagnetic tape is 0.85 to 1.00.

Regarding the cos θ, as a result of the intensive studies of theinventors, a new finding which was not known in the related art, inwhich the cos θ correlates with the difference (l_(99.9)−l_(0.1)) wasobtained. The setting of the cos θ to be 0.85 to 1.00 is one ofpreferred means for preventing the difference (l_(99.9)−l_(0.1)) to beequal to or smaller than 180 nm. The cos θ will be described later indetail.

In one aspect, the cos θ is 0.89 to 1.00.

In one aspect, the magnetic layer further includes a polyesterchain-containing compound having a weight-average molecular weight of1,000 to 80,000.

In one aspect, the difference (l_(99.9)−l_(0.1)) is equal to or smallerthan 100 nm.

In one aspect, the activation volume of the ferromagnetic hexagonalferrite powder is 800 nm³ to 1,600 nm³.

In one aspect, the magnetic tape includes a non-magnetic layer includingnon-magnetic powder and a binder, between the non-magnetic support andthe magnetic layer.

According to another aspect of the invention, there is provided amagnetic tape device comprising: the magnetic tape; a magnetic head; anda servo head.

According to one aspect of the invention, it is possible to provide amagnetic tape in which a servo pattern is formed and which has animproved head positioning accuracy of a timing-based servo system at thetime of drive running, and a magnetic tape device which records and/orreproduces a magnetic signal to the magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of disposition of data bands and servo bands.

FIG. 2 shows a servo pattern disposition example of a LTO Ultrium formattape.

FIG. 3 is an explanatory diagram of an angle α regarding an edge shapeof the servo pattern.

FIG. 4 is an explanatory diagram of another angle α regarding an edgeshape of the servo pattern.

FIG. 5 shows an example of the edge shape of the servo pattern.

FIG. 6 shows an example of the servo pattern.

FIG. 7 shows another example of the servo pattern.

FIG. 8 shows still another example of the servo pattern.

FIG. 9 is an explanatory diagram of an angle θ regarding a cos θ.

FIG. 10 is an explanatory diagram of another angle θ regarding a cos θ.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape

According to one aspect of the invention, there is provided a magnetictape including: a magnetic layer including ferromagnetic powder and abinder on a non-magnetic support, in which the magnetic layer includes atiming-based servo pattern, the ferromagnetic powder is ferromagnetichexagonal ferrite powder having an activation volume equal to or smallerthan 1,600 nm³, and an edge shape of the timing-based servo patternspecified by a magnetic force microscope observation is a shape in whicha difference (l_(99.9)−l_(0.1)) between a value l_(99.9) of a cumulativefrequency function of 99.9% of a position deviation width from an idealshape in a longitudinal direction of the magnetic tape and a valuel_(0.1) of the cumulative frequency function of 0.1% thereof is equal toor smaller than 180 nm.

Hereinafter, the magnetic tape will be further described in detail. Thespecification contains surmise of the inventors. The invention is notlimited by such surmise. In addition, in the specification, the examplesare described with reference to the drawings. However, the invention isnot limited to such exemplified aspects.

Activation Volume

The magnetic layer of the magnetic tape includes ferromagnetic hexagonalferrite powder having an activation volume equal to or smaller than1,600 nm³. As a result of the studies of the inventors, it was clearthat, in the magnetic tape including the ferromagnetic hexagonal ferritepowder having an activation volume equal to or smaller than 1,600 nm³ inthe magnetic layer, a phenomenon of a decrease in a positioning accuracyoccurs, which does not occur in a magnetic tape including ferromagnetichexagonal ferrite powder having an activation volume exceeding 1,600 nm³in a magnetic layer. Such a decrease in a positioning accuracy can beprevented by controlling the difference (l₉₉−l_(0.1)) to be equal to orsmaller than 180 nm. The difference (l_(99.9)−l_(0.1)) will be furtherdescribed later. The activation volume of the ferromagnetic hexagonalferrite powder is equal to or smaller than 1,600 nm³, and may be, forexample, equal to or smaller than 1,500 nm³ or equal to or smaller than1,400 nm³. Generally, as the activation volume decreases, high-densityrecording can be suitably performed. Here, the activation volume of theferromagnetic hexagonal ferrite powder included in the magnetic layer ofthe magnetic tape may be equal to or smaller than 1,600 nm³. Meanwhile,from a viewpoint of stability of magnetization, the lower limit of theactivation volume is preferably, for example, equal to or greater than800 nm³, and more preferably equal to or greater than 1,000 nm³, andeven more preferably equal to or greater than 1,200 nm³.

The above-mentioned activation volume of the ferromagnetic hexagonalferrite powder existing as powder can be acquired by using the powder asa measurement sample. Meanwhile, regarding the ferromagnetic hexagonalferrite powder included in the magnetic layer of the magnetic tape, ameasurement sample can be obtained by collecting powder from themagnetic layer. The collection of the measurement sample can beperformed by the following method, for example.

1. The surface treatment is performed with respect to the surface of themagnetic layer with a plasma reactor manufactured by Yamato ScientificCo., Ltd. for 1 to 2 minutes, and organic components (binder and thelike) of the surface of the magnetic layer are incinerated and removed.

2. A filter paper impregnated with an organic solvent such ascyclohexanone or acetone is attached to an edge portion of a metal bar,the surface of the magnetic layer after the treatment of the section 1.is rubbed against the upper portion thereof, and the components of themagnetic layer is transferred and stripped to the filter paper from themagnetic tape.

3. The components stripped in the section 2. are shaken off in theorganic solvent such as cyclohexanone or acetone (the filter paper isput into the organic solvent to shake off the components with anultrasonic disperser), the organic solvent is dried to extract thestripped components.

4. The components scraped in the section 3. are put into a glass testtube which is sufficiently washed, for example, approximately 20 ml ofn-butylamine is added thereto, and the glass test tube is sealed. (Theamount of n-butylamine to be added is an amount which can decompose theorganic components remaining without being incinerated.)

5. The glass test tube is heated to an internal temperature of 170° C.for 20 hours or longer, and the organic components are decomposed.

6. The precipitates after the decomposition of the section 5. aresufficiently washed with pure water and dried, and the powder isextracted.

7. A neodymium magnet is brought to be close to the powder collected inthe section 6. and the adsorbed powder (that is, ferromagnetic hexagonalferrite powder) is extracted.

By performing the steps described above, the ferromagnetic hexagonalferrite powder for measuring the activation volume can be collected fromthe magnetic layer. Since the ferromagnetic hexagonal ferrite powder isnot substantially negatively affected by performing the processesdescribed above, it is possible to measure the activation volume of theferromagnetic hexagonal ferrite powder included in the magnetic layer bythe method described above.

The ferromagnetic hexagonal ferrite powder included in the magneticlayer of the magnetic tape will be described later in detail.Hereinafter, unless otherwise noted, the ferromagnetic hexagonal ferritepowder indicates ferromagnetic hexagonal ferrite powder having anactivation volume equal to or smaller than 1,600 nm³.

Difference (l_(99.9)−l_(0.1))

The measurement and the calculation method of the difference(l_(99.9)−l_(0.1)) of the timing-based servo pattern included in themagnetic tape are as described above. As a result of the intensivestudies of the inventors, it was newly found that, in the magnetic tapeincluding the ferromagnetic hexagonal ferrite powder having anactivation volume equal to or smaller than 1,600 nm³ in the magneticlayer, by setting the difference (l_(99.9)−l_(0.1)) to be equal to orsmaller than 180 nm, it is possible to improve a head positioningaccuracy of the timing-based servo system.

The difference (l_(99.9)−l_(0.1)) is equal to or smaller than 180 nm.When the difference (l_(99.9)−l_(0.1)) is equal to or smaller than 180nm, in the magnetic tape including the ferromagnetic hexagonal ferritepowder having an activation volume equal to or smaller than 1,600 nm³ inthe magnetic layer, it is possible to improve the head positioningaccuracy of the timing-based servo system. The difference(l_(99.9)−l_(0.1)) can also be set to be, for example, equal to orsmaller than 170 nm, equal to or smaller than 160 nm, equal to orsmaller than 150 nm, equal to or smaller than 140 nm, equal to orsmaller than 130 nm, equal to or smaller than 120 nm, equal to orsmaller than 110 nm, or equal to or smaller than 100 nm. As the value ofthe difference (l_(99.9)−l_(0.1)) decreases, the head positioningaccuracy tends to be further improved. In addition, the difference(l_(99.9)−l_(0.1)) can be set to be, for example, equal to or greaterthan 50 nm, equal to or greater than 60 nm, or equal to or greater than70 nm. Here, the difference (l_(99.9)−l_(0.1)) may be equal to orsmaller than 180 nm and may be lower than the lower limit describedabove. The difference (l_(99.9)−l_(0.1)) can be controlled, for example,by the cos θ and types (specifically, leakage field) of the servo writehead used for forming the servo pattern. It is difficult to set thedifference (l_(99.9)−l_(0.1)) to be equal to or smaller than 180 nm,only by simply increasing the capacity of the servo write head(specifically, using a servo write head having a great leakage field).With respect to this, by setting the cos θ to be 0.85 to 1.00, forexample, in the magnetic tape including the ferromagnetic hexagonalferrite powder having an activation volume equal to or smaller than1,600 nm³ in the magnetic layer, it is possible to realize thedifference (l_(99.9)−l_(0.1)) equal to or smaller than 180 nm.

Cos θ

In the magnetic tape, the tilt cos θ of the ferromagnetic hexagonalferrite powder with respect to the surface of the magnetic layeracquired by the cross section observation performed by using a scanningtransmission electron microscope is preferably 0.85 to 1.00. The cos θis preferably equal to or greater than 0.89, more preferably equal to orgreater than 0.90, even more preferably equal to or greater than 0.92,and sill more preferably equal to or greater than 0.95. Meanwhile, in acase where all of the hexagonal ferrite particles having an aspect ratioand a length in a long axis direction which will be described later arepresent to be parallel to the surface of the magnetic layer, the cos θbecomes 1.00 which is the maximum value. According to the research ofthe inventors, it is found that, as the value of the cos θ increases,the value of the difference (l_(99.9)−l_(0.1)) tends to be decreased,and in the magnetic tape including the ferromagnetic hexagonal ferritepowder having an activation volume equal to or smaller than 1,600 nm³ inthe magnetic layer, it is possible to improve the head positioningaccuracy of the timing-based servo system. That is, in the magnetic tapeincluding the ferromagnetic hexagonal ferrite powder having anactivation volume equal to or smaller than 1,600 nm³ in the magneticlayer, a great value of the cos θ is preferable, from a viewpoint offurther improving the head positioning accuracy of the timing-basedservo system. Accordingly, in the magnetic tape, the upper limit of thecos θ is equal to or smaller than 1.00. The cos θ may be, for example,equal to or smaller than 0.99. However, as described above, a greatvalue of the cos θ is preferable, and thus, the cos θ may exceed 0.99.

Calculation Method of Cos θ

The cos θ is acquired by the cross section observation performed byusing a scanning transmission electron microscope (hereinafter, alsoreferred to as a “STEM”). The cos θ of the invention and thespecification is a value measured and calculated by the followingmethod.

(1) A cross section observation sample is manufactured by performing thecutting out from an arbitrarily determined position of the magnetic tapewhich is a target for acquiring the cos θ. The manufacturing of thecross section observation sample is performed by focused ion beam (FIB)processing using a gallium ion (Ga⁺) beam. A specific example of such amanufacturing method will be described later with an example.

(2) The manufactured cross section observation sample is observed withthe STEM, and a STEM images are captured. The STEM images are capturedat positions of the same cross section observation sample arbitrarilyselected, except for selecting so that the imaging ranges are notoverlapped, and total 10 images are obtained. The STEM image is aSTEM-high-angle annular dark field (HAADF) image which is captured at anacceleration voltage of 300 kV and an imaging magnification of 450,000,and the imaging is performed so that entire region of the magnetic layerin a thickness direction is included in one image. The entire region ofthe magnetic layer in the thickness direction is a region from thesurface of the magnetic layer observed in the cross section observationsample to an interface between the magnetic layer and the adjacent layeror the non-magnetic support. The adjacent layer is a non-magnetic layer,in a case where the magnetic tape which is a target for acquiring thecos θ includes the non-magnetic layer which will be described laterbetween the magnetic layer and the non-magnetic support. Meanwhile, in acase where the magnetic tape which is a target for acquiring the cos θincludes the magnetic layer directly on the non-magnetic support, theinterface is an interface between the magnetic layer and thenon-magnetic support.

(3) In each STEM image obtained as described above, a linear lineconnecting both ends of a line segment showing the surface of themagnetic layer is determined as a reference line. In a case where theSTEM image is captured so that the magnetic layer side of the crosssection observation sample is positioned on the upper side of the imageand the non-magnetic support side is positioned on the lower side, forexample, the linear line connecting both ends of the line segmentdescribed above is a linear line connecting an intersection between aleft side of the image (normally, having a rectangular or square shape)of the STEM image and the line segment, and an intersection between aright side of the STEM image and the line segment to each other.

(4) Among the hexagonal ferrite particles observed in the STEM image, anangle θ formed by the reference line and the long axis direction of thehexagonal ferrite particles (primary particles) having an aspect ratioin a range of 1.5 to 6.0 and a length in the long axis direction equalto or greater than 10 nm is measured, and regarding the measured angleθ, the cos θ is calculated as a cos θ based on a unit circuit. Thecalculation of the cos θ is performed with 30 particles arbitrarilyextracted from the hexagonal ferrite particles having the aspect ratioand the length in the long axis direction in each STEM image.

(5) The measurement and the calculation are respectively performed for10 images, the values of the acquired cos θ of the 30 hexagonal ferriteparticles of each image, that is, 300 hexagonal ferrite particles intotal of the 10 images, are averaged. The arithmetical mean acquired asdescribed above is set as the tilt cos θ of the ferromagnetic hexagonalferrite powder with respect to the surface of the magnetic layeracquired by the cross section observation performed by using thescanning transmission electron microscope.

Here, the “aspect ratio” observed in the STEM image is a ratio of“length in the long axis direction/length in a short axis direction” ofthe hexagonal ferrite particles.

The “long axis direction” means a direction when an end portion close tothe reference line and an end portion far from the reference line areconnected to each other, among the end portions which are most separatedfrom each other, in the image of one hexagonal ferrite particle observedin the STEM image. In a case where a line segment connecting one endportion and the other end portion is parallel with the reference line, adirection parallel to the reference line becomes the long axisdirection.

The “length in the long axis direction” means a length of a line segmentdrawn by connecting end portions which are most separated from eachother, in the image of one hexagonal ferrite particle observed in theSTEM image. Meanwhile, the “length in the short axis direction” means alength of the longest line segment, among the line segments connectingtwo intersections between an outer periphery of the image of theparticle and a perpendicular line with respect to the long axisdirection.

In addition, the angle θ formed by the reference line and the tilt ofthe particle in the long axis direction is determined to be in a rangeof 0° to 90°, by setting an angle of the long axis direction parallel tothe reference line as 0°. Hereinafter, the angle θ will be furtherdescribed with reference to the drawings.

FIG. 9 and FIG. 10 are explanatory diagrams of the angle θ. In FIG. 9and FIG. 10, a reference numeral 101 indicates a line segment (length inthe long axis direction) drawn by connecting end portions which are mostseparated from each other, a reference numeral 102 indicates thereference line, and a reference numeral 103 indicates an extended lineof the line segment (reference numeral 101). In this case, as the angleformed by the reference line 102 and the extended line 103, θ1 and θ2are exemplified as shown in FIG. 9 and FIG. 10. Here, a smaller angle isused from the θ1 and θ2, and this is set as the angle θ. Accordingly, inthe aspect shown in FIG. 9, the θ1 is set as the angle θ, and in theaspect shown in FIG. 10, θ2 is set as the angle θ. A case where θ1=θ2 isa case where the angle θ=90°. The cos θ based on the unit circle becomes1.00, in a case where the θ=0°, and becomes 0, in a case where theθ=90°.

A squareness ratio is known as an index of a presence state (orientationstate) of the ferromagnetic hexagonal ferrite powder of the magneticlayer. However, according to the studies of the inventors, in themagnetic tape including the ferromagnetic hexagonal ferrite powderhaving an activation volume equal to or smaller than 1,600 nm³ in themagnetic layer, an excellent correlation was not observed between thesquareness ratio and the difference (l_(99.9)−l_(0.1)) or the headpositioning accuracy of the timing-based servo system. The squarenessratio is a value indicating a ratio of residual magnetization withrespect to saturated magnetization, and is measured using all of theparticles as targets, regardless of the shapes and size of the particlesincluded in the ferromagnetic hexagonal ferrite powder. With respect tothis, the cos θ is a value measured by selecting the hexagonal ferriteparticles having the aspect ratio and the length in the longitudinaldirection in the ranges described above. With such a difference, theinventors have thought that an excellent correlation may be foundbetween the cos θ and the difference (l_(99.9)−l_(0.1)), and between thecos θ and the head positioning accuracy of the timing-based servosystem. However, this is merely a surmise, and the invention is notlimited thereto.

Adjustment Method of Cos θ

The magnetic tape can be manufactured through a step of applying amagnetic layer forming composition onto the non-magnetic support. As anadjustment method of the cos θ, a method of controlling a dispersionstate of the ferromagnetic hexagonal ferrite powder of the magneticlayer forming composition is used. Regarding this viewpoint, theinventors have thought that, as dispersibility of the ferromagnetichexagonal ferrite powder having an activation volume equal to or smallerthan 1,600 nm³ in the magnetic layer forming composition (hereinafter,also simply referred to as “dispersibility of the ferromagnetichexagonal ferrite powder” or “dispersibility”) is increased, thehexagonal ferrite particles having the aspect ratio and the length inthe long axis direction in the ranges described above in the magneticlayer formed by using this magnetic layer forming composition are easilyoriented in a state closer to parallel to the surface of the magneticlayer. As means for increasing dispersibility, any one or both of thefollowing methods (1) and (2) are used.

(1) Adjustment of Dispersion Conditions

(2) Use of Dispersing Agent

In addition, in the magnetic tape including an abrasive in the magneticlayer, as means for increasing dispersibility, a method of separatelydispersing the ferromagnetic hexagonal ferrite powder and the abrasiveis also used. The separate dispersing is more specifically a method ofpreparing the magnetic layer forming composition through a step ofmixing a magnetic solution including the ferromagnetic hexagonal ferritepowder having an activation volume equal to or smaller than 1,600 nm³, abinder, and a solvent (here, substantially not including an abrasive),and an abrasive liquid including an abrasive and a solvent with eachother. By performing the mixing after separately dispersing the abrasiveand the ferromagnetic hexagonal ferrite powder as described above, it ispossible to increase the dispersibility of the ferromagnetic hexagonalferrite powder of the magnetic layer forming composition. The expressionof “substantially not including an abrasive” means that the abrasive isnot added as a constituent component of the magnetic solution, and asmall amount of the abrasive present as impurities by being mixedwithout intention is allowed. In addition, it is also preferable thatany one or both of the methods (1) and (2) are combined with theseparate dispersing described above. In this case, by controlling thedispersion state of the ferromagnetic hexagonal ferrite powder of themagnetic solution, it is possible to control the dispersion state of theferromagnetic hexagonal ferrite powder of the magnetic layer formingcomposition obtained through the step of mixing the magnetic solutionwith the abrasive liquid.

Hereinafter, specific aspects of the methods (1) and (2) will bedescribed.

(1) Adjustment of Dispersion Conditions

A dispersing process of the magnetic layer forming composition,preferably the magnetic solution can be performed by adjusting thedispersion conditions thereof by using a well-known dispersing method.The dispersion conditions of the dispersing process, for example,include the types of a dispersion device, the types of dispersion mediaused in the dispersion device, and a retention time in the dispersiondevice (hereinafter, also referred to as a “dispersion retention time”).

As the dispersion device, various well-known dispersion devices using ashear force such as a ball mill, a sand mill, or a homomixer. Adispersing process having two or more stages may be performed byconnecting two or more dispersion devices to each other, or differentdispersion devices may be used in combination. A circumferential speedof a tip of the dispersion device is preferably 5 to 20 m/sec and morepreferably 7 to 15 m/sec.

As the dispersion medium, ceramic beads or glass beads are used, andzirconia beads are preferable. Two or more types of beads may be used incombination. A particle diameter of the dispersion medium is, forexample, 0.03 to 1 mm and is preferably 0.05 to 0.5 mm. In a case ofperforming the dispersing process having two or more stages byconnecting the dispersion devices as described above, the dispersionmedium having different particle diameters may be used in each stage. Itis preferable that the dispersion medium having a smaller particlediameter is used, as the stages are passed. A filling percentage of thedispersion medium can be, for example, 30% to 80% and preferably 50% to80% based on the volume.

The dispersion retention time may be suitably set b considering thecircumferential speed of the tip of the dispersion device and thefilling percentage of the dispersion medium, and can be, for example, 15to 45 hours and preferably 20 hours to 40 hours. In a case of performingthe dispersing process having two or more stages by connecting thedispersion devices as described above, the total dispersion retentiontime of each stage is preferably in the range described above. Byperforming the dispersing process described above, it is possible toincrease the dispersibility of the ferromagnetic hexagonal ferritepowder and to adjust the cos θ to be 0.85 to 1.00.

(2) Use of Dispersing Agent

It is possible to increase the dispersibility of the ferromagnetichexagonal ferrite powder by using a dispersing agent at the time ofpreparing the magnetic layer forming composition, preferably at the timeof preparing the magnetic solution. Here, the dispersing agent is acomponent which can increase the dispersibility of the ferromagnetichexagonal ferrite powder of the magnetic layer forming compositionand/or the magnetic solution, compared to a state where the agent is notpresent. It is also possible to control the dispersion state of theferromagnetic hexagonal ferrite powder by changing the type and theamount of the dispersing agent included in the magnetic layer formingcomposition and/or the magnetic solution. As the dispersing agent, adispersing agent which prevents aggregation of the hexagonal ferriteparticles configuring the ferromagnetic hexagonal ferrite powder andimparts suitable plasticity to the magnetic layer is also preferablyused, from a viewpoint of increasing durability of the magnetic layer.

As an aspect of the dispersing agent preferable for improving thedispersibility of the ferromagnetic hexagonal ferrite powder having anactivation volume equal to or smaller than 1,600 nm³, a polyesterchain-containing compound can be used. The polyester chain-containingcompound is preferable from a viewpoint of imparting suitable plasticityto the magnetic layer. Here, the polyester chain is shown as E inGeneral Formula A which will be described later. Specific aspectsthereof include a polyester chain contained in General Formula 1, apolyester chain represented by Formula 2-A, and a polyester chainrepresented by Formula 2-B which will be described later. The inventorshave surmised that, by mixing the polyester chain-containing componentwith the magnetic layer forming composition and/or the magnetic solutiontogether with the ferromagnetic hexagonal ferrite powder, it is possibleto prevent aggregation of particles, due to the polyester chaininterposed between the hexagonal ferrite particles. However, this ismerely the surmise, and the invention is not limited thereto. Aweight-average molecular weight of the polyester chain-containingcompound is preferably equal to or greater than 1,000, from a viewpointof improving the dispersibility of the ferromagnetic hexagonal ferritepowder. In addition, the weight-average molecular weight of thepolyester chain-containing compound is preferably equal to or smallerthan 80,000. The inventors have thought that the polyesterchain-containing compound having a weight-average molecular weight equalto or smaller than 80,000 can increase the durability of the magneticlayer by exhibiting an operation of a plasticizer. The weight-averagemolecular weight of the invention and the specification is a valueobtained by performing polystyrene conversion of a value measured by gelpermeation chromatography (GPC). Specific examples of the measurementconditions will be described later. In addition, the preferred range ofthe weight-average molecular weight will be also described later.

As a preferred aspect of the polyester chain-containing compound, acompound having a partial structure represented by the following GeneralFormula A is used. In the invention and the specification, unlessotherwise noted, a group disclosed may include a substituent or may benon-substituted. In a case where a given group includes a substituent,examples of the substituent include an alkyl group (for example, alkylgroup having 1 to 6 carbon atoms), a hydroxyl group, an alkoxy group(for example, alkoxy group having 1 to 6 carbon atoms), a halogen atom(for example, a fluorine atom, a chlorine atom, or a bromine atom), acyano group, an amino group, a nitro group, an acyl group, carboxyl(salt) group. In addition, the “number of carbon atoms” of the groupincluding a substituent means the number of carbon atoms of a portionnot including a substituent.[T-Q-E

_(b) ^(*)  General Formula A

In General Formula A, Q represents —O—, —CO—, —S—, —NR^(a)—, or a singlebond, T and R^(a) each independently represent a hydrogen atom or amonovalent substituent, E represents —(O-L^(A)-CO)a- or —(CO-L^(A)-O)a-,L^(A) represents a divalent linking group, a represents an integer equalto or greater than 2, b represents an integer equal to or greater than1, and * represents a bonding site with another partial structureconfiguring the polyester chain-containing compound.

In General Formula A, the number of L^(A) included is a value of a×b. Inaddition, the numbers of T and Q included are respectively the value ofb. In a case where a plurality of L^(A) are included in General FormulaA, the plurality of L^(A) may be the same as each other or differentfrom each other. The same applies to T and Q.

It is considered that the compound described above can preventaggregation of hexagonal ferrite particles due to a steric hindrancecaused by the partial structure, in the magnetic solution and themagnetic layer forming composition.

As a preferred aspect of the polyester chain-containing component, acompound including a group which can be adsorbed to the surface of thehexagonal ferrite particles or the partial structure (hereinafter,referred to as an “adsorption part”) together with the polyester chainin a molecule is used. It is preferable that the polyester chain isincluded in the partial structure represented by General Formula A. Inaddition, it is more preferable that the partial structure and theadsorption part represented by General Formula A form a bond through *in General Formula A.

In one aspect, the adsorption part can be a functional group (polargroup) having polarity to be an adsorption point to the surface of thehexagonal ferrite particles. As a specific example, at least one polargroup selected from a carboxyl group (—COOH) and a salt thereof(—COO⁻M⁺), a sulfonic acid group (—SO₃H) and a salt thereof (—SO₃ ⁻M⁺),a sulfuric acid group (—OSO₃H) and a salt thereof (—OSO₃ ⁻M⁺), aphosphoric acid group (—P═O(OH)₂) and a salt thereof (—P—O(O⁻M⁺)₂), anamino group (—NR₂), —N⁺R₃, an epoxy group, a thiol group (—SH), and acyano group (—CN) (here, M⁺ represents a cation such as an alkali metalion and R represents a hydrogen atom or a hydrocarbon group) can beused. In addition, the “carboxyl (salt) group” means one or both of acarboxyl group and a slat thereof (carboxylic salt). The carboxylic saltis a state of a salt of the carboxyl group (—COOH) as described above.

As one aspect of the adsorption part, a polyalkyleneimine chain can alsobe used.

The types of the bond formed by the partial structure and the adsorptionpart represented by General Formula A are not particularly limited. Sucha bond is preferably selected from a covalent bond, a coordinate bond,and an ion bond, and a bond of different types may be included in thesame molecular. It is considered that by efficiently performing theadsorption with respect to the hexagonal ferrite particles through theadsorption part, it is possible to further increase an aggregationprevention effect of the hexagonal ferrite particles based on the sterichindrance caused by the partial structure represented by General FormulaA.

In one aspect, the polyester chain-containing compound can include atleast one polyalkyleneimine chain. The polyester chain-containingcompound can preferably include a polyester chain in the partialstructure represented by General Formula A. As a preferred example ofthe polyester chain-containing compound, a polyalkyleneimine derivativeincluding a polyester chain selected from the group consisting of apolyester chain represented by the following Formula 2-A and a polyesterchain represented by the following Formula 2-B as General Formula A isused. These examples will be described later in detail.

L¹ in Formula 2-A and L² in Formula 2-B each independently represent adivalent linking group, b11 in Formula 2-A and b21 in Formula 2-B eachindependently represent an integer equal to or greater than 2, b12 inFormula 2-A and b22 in Formula 2-B each independently represent 0 or 1,and X¹ in Formula 2-A and X² in Formula 2-B each independently representa hydrogen atom or a monovalent substituent.

In General Formula A, Q represents —O—, —CO—, —S—, —NR^(a)—, or a singlebond, and is preferably a portion represented by X in General Formula 1which will be described later, (—CO—)b12 in Formula 2-A or (—CO—)b22 inFormula 2-B.

In General Formula A, T and R^(a) each independently represent ahydrogen atom or a monovalent substituent and is preferably a portionrepresented by R in General Formula 1 which will be described later, X¹in Formula 2-A or X² in Formula 2-B.

In General Formula A, E represents —(O-L^(A)-CO)a- or —(CO-L^(A)-O)a-,L^(A) represents a divalent linking group, and a represents an integerequal to or greater than 2.

As a divalent linking group represented by L^(A), L in General Formula 1which will be described later, L¹ in Formula 2-A or L² in Formula 2-B ispreferably used.

In one aspect, the polyester chain-containing compound can include atleast one group selected from the group consisting of a carboxyl groupand a carboxylic salt. Such a polyester chain-containing compound canpreferably include a polyester chain in the partial structurerepresented by General Formula A. As a preferred example of thepolyester chain-containing compound, a compound represented by thefollowing General Formula 1 is used.

Compound Represented by General Formula 1

General Formula 1 is as described below.

(In General Formula 1, X represents —O—, —S—, or —NR¹—, R and R¹ eachindependently represent a hydrogen atom or a monovalent substituent, Lrepresents a divalent linking group, Z represents a n-valent partialstructure including at least one group (carboxylic (salt) group)selected from the group consisting of a carboxyl group and a carboxylicsalt, m represents an integer equal to or greater than 2, and nrepresents an integer equal to or greater than 1.)

In General Formula 1, the number of L included is a value of m×n. Inaddition, the numbers of R and X included are respectively the value ofn. In a case where a plurality of L are included in General Formula 1,the plurality of L may be the same as each other or different from eachother. The same applies to R and X.

The compound represented by General Formula 1 has a structure (polyesterchain) represented by —((C═O)-L-O)m-, and a carboxylic (salt) group isincluded in the Z part as the adsorption part. It is considered that,when the compound represented by General Formula 1 is effectivelyadsorbed to the hexagonal ferrite particles by setting the carboxylic(salt) group included in the Z part as the adsorption part to thesurface of the hexagonal ferrite particles, it is possible to preventaggregation of the hexagonal ferrite particles caused by sterichindrance caused by the polyester chain.

In General Formula 1, X represents —O—, —S—, or —NR¹—, and R¹ representsa hydrogen atom or a monovalent substituent. As the monovalentsubstituent represented by R¹, an alkyl group, a hydroxyl group, analkoxy group, a hydrogen atom, a cyano group, an amino group, a nitrogroup, an acyl group, and a carboxyl (salt) group which is thesubstituent described above can be used, an alkyl group is preferablyused, an alkyl group having 1 to 6 carbon atoms is more preferably used,and a methyl group or an ethyl group is even more preferably used. R¹ isstill more preferably a hydrogen atom. X preferably represents —O—.

R represents a hydrogen atom or a monovalent substituent. R preferablyrepresents a monovalent substituent. As the monovalent substituentrepresented by R, a monovalent group such as an alkyl group, an arylgroup, a heteroaryl group, an alicyclic group, or a nonaromaticheterocyclic group, and a structure in which a divalent linking group isbonded to the monovalent group (that is, R has a structure in which adivalent linking group is bonded to the monovalent group and is amonovalent substituent bonding with X through the divalent linkinggroup) can be used, for example. As the divalent linking group, adivalent linking group configured of a combination of one or two or moreselected from the group consisting of —C(═O)—O—, —O—, —C(═O)—NR¹⁰— (R¹⁰represents a hydrogen atom or an alkyl group having 1 to 4 carbonatoms), —O—C(═O)—NH—, a phenylene group, an alkylene group having 1 to30 carbon atoms, and an alkenylene group having 2 to 30 carbon atoms canbe used, for example. As a specific example of the monovalentsubstituent represented by R, the following structure is used, forexample. In the following structures, * represents a bonding site withX. However, R is not limited to the following specific example.

In General Formula 1, L represents a divalent linking group. As thedivalent linking group, a divalent linking group which is configured ofa combination of one or two or more selected from the group consistingof an alkylene group which may have a linear, branched, or cyclicstructure, an alkenylene group which may have a linear, branched, orcyclic structure, —C(═O)—, —O—, and an arylene group, and which mayinclude a substituent in the divalent linking group or a halogen atom asan anion can be used. More specifically, a divalent linking groupconfigured of a combination of one or two or more selected from analkylene group having 1 to 12 carbon atoms which may have a linear,branched, or cyclic structure, an alkenylene group having 1 to 6 carbonatoms which may have a linear, branched, or cyclic structure, —C(═O)—,—O—, and a phenylene group can be used. The divalent linking group ispreferably a divalent linking group formed of 1 to 10 carbon atoms, 0 to10 oxygen atoms, 0 to 10 halogen atoms, and 1 to 30 hydrogen atoms. As aspecific example, an alkylene group and the following structure areused. In the following structures, * represents a bonding site with theother structure in General Formula 1. However, the divalent linkinggroup is not limited to the following specific example.

L is preferably an alkylene group, more preferably an alkylene grouphaving 1 to 12 carbon atoms, even more preferably an alkylene grouphaving 1 to 5 carbon atoms, and still more preferably a non-substitutedalkylene group having 1 to 5 carbon atoms.

Z represents an n-valent partial structure including at least one group(carboxylic (salt) group) selected from the group consisting of acarboxyl group and a carboxylic salt.

The number of the carboxylic (salt) group included in Z is at least 1,preferably equal to or greater than 2, and more preferably 2 to 4, forone Z.

Z can have a structure of one or more selected from the group consistingof a linear structure, a branched structure, and a cyclic structure.From a viewpoint of easiness of synthesis, Z is preferably a reactiveresidue of a carboxylic acid anhydride. For example, as a specificexample, the following structure is used. In the following structures, *represents a bonding site with the other structure in General Formula 1.However, Z is not limited to the following specific example.

The carboxylic acid anhydride is a compound having a partial structurerepresented by —(C═O)—O—(C═O)—. In the carboxylic acid anhydride, thepartial structure becomes a reactive site, and an oxygen atom and Z of—((C═O)-L-O)m- in General Formula 1 are bonded to each other through acarbonyl bond (—(C═O)—), and a carboxylic (salt) group is obtained. Thepartial structure generated as described above is a reactive residue ofa carboxylic acid anhydride. By synthesizing the compound represented byGeneral Formula 1 by using a compound having one partial structure—(C═O)—O—(C═O)—, as the carboxylic acid anhydride, it is possible toobtain a compound represented by General Formula 1 including amonovalent reactive residue of the carboxylic acid anhydride, and it ispossible to obtain a compound represented by General Formula 1 includinga divalent reactive residue of the carboxylic acid anhydride, by usingthe compound having two partial structures described above. The sameapplies to the compound represented by General Formula 1 including atrivalent reactive residue of the carboxylic acid anhydride. Asdescribed above, n is an integer equal to or greater than 1, is, forexample, an integer of 1 to 4, and is preferably an integer of 2 to 4.

It is possible to obtain a compound represented by General Formula 1 ina case of n=2, by using the tetracarboxylic acid anhydride, for example,as the carboxylic acid anhydride. The tetracarboxylic acid anhydride isa carboxylic acid anhydride having two partial structures describedabove in one molecule, by dehydration synthesis of two carboxyl groups,in the compound including four carboxyl groups in one molecule. InGeneral Formula 1, the compound in which Z represents a reactive residueof the tetracarboxylic acid anhydride is preferable, from viewpoints offurther improving dispersibility of ferromagnetic hexagonal ferritepowder and durability of the magnetic layer. Examples of thetetracarboxylic acid anhydride include various tetracarboxylic acidanhydrides such as aliphatic tetracarboxylic acid anhydride, aromatictetracarboxylic acid anhydride, and polycyclic tetracarboxylic acidanhydride.

As the aliphatic tetracarboxylic acid anhydride, for example, variousaliphatic tetracarboxylic acid anhydrides disclosed in a paragraph 0040of JP2016-071926A can be used. As the aromatic tetracarboxylic acidanhydride, for example, various aromatic tetracarboxylic acid anhydridesdisclosed in a paragraph 0041 of JP2016-071926A can be used. As thepolycyclic tetracarboxylic acid anhydride, various polycyclictetracarboxylic acid anhydrides disclosed in a paragraph 0042 ofJP2016-071926 can be used.

In General Formula 1, m represents an integer equal to or greater than2. As described above, it is though that the structure (polyester chain)represented by —((C═O)-L-O)m- of the compound represented by GeneralFormula 1 contributes to the improvement of dispersibility and thedurability. From these viewpoints, m is preferably an integer of 5 to200, more preferably an integer of 5 to 100, and even more preferably aninteger of 5 to 60.

Weight-Average Molecular Weight

The weight-average molecular weight of the compound represented byGeneral Formula 1 is preferably 1,000 to 80,000 as described above andmore preferably 1,000 to 20,000. The weight-average molecular weight ofthe compound represented by General Formula 1 is even more preferablysmaller than 20,000, further more preferably equal to or smaller than12,000, and sill more preferably equal to or smaller than 10,000. Inaddition, the weight-average molecular weight of the compoundrepresented by General Formula 1 is preferably equal to or greater than1,500 and more preferably equal to or greater than 2,000. Regarding thecompound represented by General Formula 1, the weight-average molecularweight shown in examples which will be described later is a valueobtained by performing reference polystyrene conversion of a valuemeasured by GPC under the following measurement conditions. In addition,the weight-average molecular weight of a mixture of two or more kinds ofstructural isomers is a weight-average molecular weight of two or morekinds of structural isomers included in this mixture.

GPC device: HLC-8220 (manufactured by Tosoh Corporation)

Guard column: TSK guard column Super HZM-H

Column: TSK gel Super HZ 2000, TSK gel Super HZ 4000, TSK gel Super HZ-M(manufactured by Tosoh Corporation, 4.6 mm (inner diameter)×15.0 cm,three types of columns are connected in series)

Eluent: Tetrahydrofuran (THF), containing a stabilizer(2,6-di-t-butyl-4-methylphenol)

Flow rate of eluent: 0.35 mL/min

Column temperature: 40° C.

Inlet temperature: 40° C.

Refractive index (RI) measurement temperature: 40° C.

Sample concentration: 0.3 mass %

Sample introduction amount: 10 μL

Analysis Method

The compound represented by General Formula 1 described above can besynthesized by a well-known method. As an example of the synthesismethod, a method of allowing a reaction such as a ring-opening additionreaction between the carboxylic acid anhydride and a compoundrepresented by the following General Formula 2 can be used, for example.In General Formula 2, R, X, L, and m are the same as those in GeneralFormula 1. A represents a hydrogen atom, an alkali metal atom, orquaternary ammonium base and is preferably a hydrogen atom.

In a case of using a butanetetracarboxylic acid anhydride, for example,the reaction between the carboxylic acid anhydride and a compoundrepresented by the following General Formula 2 is performed by mixingthe butanetetracarboxylic acid anhydride at a percentage of 0.4 to 0.5moles with respect to 1 equivalent of a hydroxyl group, and heating andstirring the mixture approximately for 3 to 12 hours, under the absenceof solvent, if necessary, under the presence of an organic solventhaving a boiling point equal to or higher than 50° C., further, acatalyst such as tertiary amine or inorganic base. Even in a case ofusing other carboxylic acid anhydride, a reaction between the carboxylicacid anhydride and the compound represented by General Formula 2 can beperformed under the reaction conditions described above or underwell-known reaction conditions.

After the reaction, post-process such as purification may be performed,if necessary.

In addition, the compound represented by General Formula 2 can also beobtained by using a commercially available product or by a well-knownpolyester synthesis method. For example, as the polyester synthesismethod, ring-opening polymerization of lactone can be used. As thering-opening polymerization of lactone, descriptions disclosed inparagraphs 0050 to 0051 of JP2016-071926A can be referred to. However,the compound represented by General Formula 2 is not limited to acompound obtained by the ring-opening polymerization of lactone, and canalso be a compound obtained by a well-known polyester synthesis method,for example, polycondensation of polyvalent carboxylic acid andpolyhydric alcohol or polycondensation of hydroxycarboxylic acid.

The synthesis method described above is merely an example and there isno limitation regarding the synthesis method of the compound representedby General Formula 1. Any well-known synthesis method can be usedwithout limitation, as long as it is a method capable of synthesizingthe compound represented by General Formula 1. The reaction productafter the synthesis can be used for forming the magnetic layer, as itis, or by purifying the reaction product by a well-known method, ifnecessary. The compound represented by General Formula 1 may be usedalone or in combination of two or more kinds having differentstructures, in order to form the magnetic layer. In addition, thecompound represented by General Formula 1 may be used as a mixture oftwo or more kinds of structural isomers. For example, in a case ofobtaining two or more kinds of structural isomers by the synthesisreaction of the compound represented by General Formula 1, the mixturecan also be used for forming the magnetic layer.

As the compound represented by General Formula 1, various compoundsincluded in reaction products shown in synthesis examples in examplesdisclosed in JP2016-071926 can be used. For example, as a specificexample thereof, compounds shown in the following Table 1 can be used. Aweight-average molecular weight shown in Table 1 is a weight-averagemolecular weight of the compound represented by structural formula shownin Table 1 or a weight-average molecular weight of the compoundrepresented by structural formula shown in Table 1 and a mixture ofstructural isomers thereof.

TABLE 1 Weight- average molecular Types Structural Formula weight Com-pound 1

9200 Com- pound 2

6300 Com- pound 3

5300 Com- pound 4

8000 Com- pound 5

8700 Com- pound 6

8600 Com- pound 7

6200 Com- pound 8

8000

As an aspect of a preferred example of the compound having the partialstructure and the adsorption part represented by General Formula A, apolyalkyleneimine derivative including a polyester chain represented bythe following Formula 2-A or 2-B as General Formula A is used.Hereinafter, the polyalkyleneimine derivative will be described.

Polyalkyleneimine Derivative

The polyalkyleneimine derivative is a compound including at least onepolyester chain selected from the group consisting of a polyester chainrepresented by the following Formula 2-A and a polyester chainrepresented by the following Formula 2-B, and a polyalkyleneimine chainhaving a number average molecular weight of 300 to 3,000. A percentageof the polyalkyleneimine chain occupying the compound is preferablysmaller than 5.0 mass %.

The polyalkyleneimine derivative includes a polyalkyleneimine chainwhich is an aspect of the adsorption part described above. In addition,it is thought that, the steric hindrance caused by the polyester chainincluded in the polyalkyleneimine derivative is caused in the magneticlayer forming composition and/or the magnetic solution, and accordingly,it is possible to prevent aggregation of the hexagonal ferriteparticles.

Hereinafter, the polyester chain and the polyalkyleneimine chainincluded in the polyalkyleneimine derivative will be described.

Polyester Chain

Structure of Polyester Chain

The polyalkyleneimine derivative includes at least one polyester chainselected from the group consisting of a polyester chain represented bythe following Formula 2-A and a polyester chain represented by thefollowing Formula 2-B, together with a polyalkyleneimine chain whichwill be described later. In one aspect, the polyester chain is bonded toan alkyleneimine chain represented by Formula A which will be describedlater by a nitrogen atom N included in Formula A and a carbonyl bond—(C═O)— at *¹ of Formula A, and —N—(C═O)— can be formed. In addition, inanother aspect, an alkyleneimine chain represented by Formula B whichwill be described later and the polyester chain can form a saltcrosslinking group by a nitrogen cation N⁺ in Formula B and an anionicgroup including a polyester chain. As the salt crosslinking group, acomponent formed by an oxygen anion O⁻ included in the polyester chainand N⁺ in Formula B can be used.

As the polyester chain bonded to the alkyleneimine chain represented byFormula A by a nitrogen atom N included in Formula A and a carbonyl bond—(C═O)—, the polyester chain represented by Formula 2-A can be used. Thepolyester chain represented by Formula 2-A can be bonded to thealkyleneimine chain represented by Formula A by forming —N—(C═O)— by anitrogen atom included in the alkyleneimine chain and a carbonyl group—(C═O)— included in the polyester chain at the bonding site representedby *¹.

In addition, as the polyester chain bonded to the alkyleneimine chainrepresented by Formula B by forming a salt crosslinking group by N⁺ inFormula B and an anionic group including the polyester chain, thepolyester chain represented by Formula 2-B can be used. The polyesterchain represented by Formula 2-B can form N⁺ in Formula B and a saltcrosslinking group by an oxygen anion O⁻.

L¹ in Formula 2-A and L² in Formula 2-B each independently represent adivalent linking group. As the divalent linking group, an alkylene grouphaving 3 to 30 carbon atoms can be preferably used. In a case where thealkylene group includes a substituent, the number of carbon atoms of thealkylene group is the number of carbon atoms of a part (main chain part)excluding the substituent, as described above.

b11 in Formula 2-A and b21 Formula 2-B each independently represent aninteger equal to or greater than 2, for example, an integer equal to orsmaller than 200. The number of lactone repeating units shown in Table 3which will be described later corresponds to b11 in Formula 2-A or b21Formula 2-B.

b12 in Formula 2-A and b22 Formula 2-B each independently represent 0 or1.

X¹ in Formula 2-A and X² Formula 2-B each independently represent ahydrogen atom or a monovalent substituent. As the monovalentsubstituent, a monovalent substituent selected from the group consistingof an alkyl group, a haloalkyl group (for example, fluoroalkyl group),an alkoxy group, a polyalkyleneoxyalkyl group, and an aryl group can beused.

The alkyl group may include a substituent or may be non-substituted. Asthe alkyl group including a substituent, an alkyl group (hydroxyalkylgroup) substituted with a hydroxyl group, and an alkyl group substitutedwith one or more halogen atoms are preferable. In addition, an alkylgroup (haloalkyl group) in which all of hydrogen atoms bonded to carbonatoms are substituted with halogen atoms is also preferable. As thehalogen atom, a fluorine atom, a chlorine atom, or a bromine atom can beused. The alkyl group is more preferably an alkyl group having 1 to 30carbon atoms, and even more preferably an alkyl group having 1 to 10carbon atoms. The alkyl group may have any of a linear, branched, andcyclic structure. The same applies to the haloalkyl group.

Specific examples of substituted or non-substituted alkyl group orhaloalkyl group include a methyl group, an ethyl group, a propyl group,a butyl group, a pentyl group, a hexyl group, a heptyl group, an octylgroup, a nonyl group, a decyl group, a undecyl group, a dodecyl group, atridecyl group, a pentadecyl group, a hexadecyl group, a heptadecylgroup, an octadecyl group, an eicosyl group, an isopropyl group, anisobutyl group, an isopentyl group, a 2-ethylhexyl group, a tert-octylgroup, a 2-hexyldecyl group, a cyclohexyl group, a cyclopentyl group, acyclohexylmethyl group, an octylcyclohexyl group, a 2-norbornyl group, a2,2,4-trimethylpentyl group, an acetylmethyl group, an acetylethylgroup, a hydroxymethyl group, a hydroxyethyl group, a hydroxypropylgroup, a hydroxybutyl group, a hydroxypentyl group, a hydroxyhexylgroup, a hydroxyheptyl group, a hydroxyoctyl group, a hydroxynonylgroup, a hydroxydecyl group, a chloromethyl group, a dichloromethylgroup, a trichloromethyl group, a bromomethyl group, a1,1,1,3,3,3-hexafluoroisopropyl group, a heptafluoropropyl group, apentadecafluoroheptyl group, a nonadecafluorononyl group, ahydroxyundecyl group, a hydroxydodecyl group, a hydroxypentadecyl group,a hydroxyheptadecyl group, and a hydroxyoctadecyl group.

Examples of the alkoxy group include a methoxy group, an ethoxy group, apropyloxy group, a hexyloxy group, a methoxyethoxy group, amethoxyethoxyethoxy group, and a methoxyethoxyethoxymethyl group.

The polyalkyleneoxyalkyl group is a monovalent substituent representedby R¹⁰(OR¹¹)n1(O)m1-. R¹⁰ represents an alkyl group, R¹¹ represents analkylene group, n1 represents an integer equal to or greater than 2, andm1 represents 0 or 1.

The alkyl group represented by R¹⁰ is as described regarding the alkylgroup represented by X¹ or X². For the specific description of the alkylgroup represented by R¹¹, the description regarding the alkyl grouprepresented by X¹ or X² can be applied by replacing the alkyl group withan alkylene group obtained by removing one hydrogen atom from thealkylene group (for example, by replacing the methyl group with amethylene group). n1 is an integer equal to or greater than 2, forexample, is an integer equal to or smaller than 10, and preferably aninteger equal to or smaller than 5.

The aryl group may include a substituent or may be annelated, and morepreferably an aryl group having 6 to 24 carbon atoms, and examplesthereof include a phenyl group, a 4-methylphenyl group, 4-phenylbenzoicacid, a 3-cyanophenyl group, a 2-chlorophenyl group, and a 2-naphthylgroup.

The polyester chain represented by the following Formula 2-A and thepolyester chain represented by the following Formula 2-B can have apolyester-derived structure obtained by a well-known polyester synthesismethod. As the polyester synthesis method, ring-opening polymerizationof lactone disclosed in paragraphs 0056 and 0057 of JP2015-28830A can beused. However, the structure of the polyester chain is not limited tothe polyester-derived structure obtained by the ring-openingpolymerization of lactone, and can be a polyester-derived structureobtained by a well-known polyester synthesis method, for example,polycondensation of polyvalent carboxylic acid and polyhydric alcohol orpolycondensation of hydroxycarboxylic acid.

Number Average Molecular Weight of Polyester Chain

A number average molecular weight of the polyester chain is preferablyequal to or greater than 200, more preferably equal to or greater than400, and even more preferably equal to or greater than 500, from aviewpoint of improvement of dispersibility of ferromagnetic hexagonalferrite powder. In addition, from the same viewpoint, the number averagemolecular weight of the polyester chain is preferably equal to orsmaller than 100,000 and more preferably equal to or smaller than50,000. As described above, it is considered that the polyester chainfunctions to cause steric hindrance in the magnetic layer formingcomposition and/or the magnetic solution and preventing the aggregationof the hexagonal ferrite particles. It is assumed that the polyesterchain having the number average molecular weight described above canexhibit such an operation in an excellent manner. The number averagemolecular weight of the polyester chain is a value obtained byperforming reference polystyrene conversion of a value measured by GPC,regarding polyester obtained by hydrolysis of a polyalkyleneiminederivative.

The value acquired as described above is the same as a value obtained byperforming reference polystyrene conversion of a value measured by GPCregarding polyester used for synthesis of the polyalkyleneiminederivative. Accordingly, the number average molecular weight acquiredregarding polyester used for synthesis of the polyalkyleneiminederivative can be used as the number average molecular weight of thepolyester chain included in the polyalkyleneimine derivative. For themeasurement conditions of the number average molecular weight of thepolyester chain, the measurement conditions of the number averagemolecular weight of polyester in a specific example which will bedescribed later can be referred to.

Polyalkyleneimine Chain

Number Average Molecular Weight

The number average molecular weight of the polyalkyleneimine chainincluded in the polyalkyleneimine derivative is a value obtained byperforming reference polystyrene conversion of a value measured by GPC,regarding polyalkyleneimine obtained by hydrolysis of apolyalkyleneimine derivative. The value acquired as described above isthe same as a value obtained by performing reference polystyreneconversion of a value measured by GPC regarding polyalkyleneimine usedfor synthesis of the polyalkyleneimine derivative. Accordingly, thenumber average molecular weight acquired regarding polyalkyleneimineused for synthesis of the polyalkyleneimine derivative can be used asthe number average molecular weight of the polyalkyleneimine chainincluded in the polyalkyleneimine derivative. For the measurementconditions of the number average molecular weight of thepolyalkyleneimine chain, a specific example which will be describedlater can be referred to. In addition, the polyalkyleneimine is apolymer which can be obtained by ring-opening polymerization ofalkyleneimine. In the polyalkyleneimine derivative, the term “polymer”is used to include a homopolymer including a repeating unit in the samestructure and a copolymer including a repeating unit in two or morekinds of different structures.

The hydrolysis of the polyalkyleneimine derivative can be performed byvarious methods which are normally used as a hydrolysis method of ester.For details of such a method, description of a hydrolysis methoddisclosed in “The Fifth Series of Experimental Chemistry Vol. 14Synthesis of Organic Compounds II—Alcohol—Amine” (Chemical Society ofJapan, Maruzen Publication, issued August, 2005) pp. 95 to 98, anddescription of a hydrolysis method disclosed in “The Fifth Series ofExperimental Chemistry Vol. 16 Synthesis of Organic CompoundsTV—Carboxylic acid—Amino Acid—Peptide” (Chemical Society of Japan,Maruzen Publication, issued March, 2005) pp. 10 to 15 cam be referredto, for example.

The polyalkyleneimine is decomposed from the obtained hydrolyzate bywell-known separating means such as liquid chromatography, and thenumber average molecular weight thereof can be acquired.

The number average molecular weight of the polyalkyleneimine chainincluded in the polyalkyleneimine derivative is in a range of 300 to3,000. The inventors have surmised that when the number averagemolecular weight of the polyalkyleneimine chain is in the rangedescribed above, the polyalkyleneimine derivative can be effectivelyadsorbed to the surface of the hexagonal ferrite particles. The numberaverage molecular weight of the polyalkyleneimine chain is preferablyequal to or greater than 500, from a viewpoint of adsorption propertiesto the surface of the hexagonal ferrite particles. From the sameviewpoint, the number average molecular weight is preferably equal to orsmaller than 2,000.

Percentage of Polyalkyleneimine Chain Occupying PolyalkyleneimineDerivative

As described above, the inventors have considered that thepolyalkyleneimine chain included in the polyalkyleneimine derivative canfunction as an adsorption part to the surface of the hexagonal ferriteparticles. A percentage of the polyalkyleneimine chain occupying thepolyalkyleneimine derivative (hereinafter, also referred to as a“polyalkyleneimine chain percentage”) is preferably smaller than 5.0mass %, from a viewpoint of increasing the dispersibility of theferromagnetic hexagonal ferrite powder. From a viewpoint of improvingthe dispersibility of the ferromagnetic hexagonal ferrite powder, thepolyalkyleneimine chain percentage is more preferably equal to orsmaller than 4.9 mass %, even more preferably equal to or smaller than4.8 mass %, further more preferably equal to or smaller than 4.5 mass %,still more preferably equal to or smaller than 4.0 mass %, and stilleven more preferably equal to or smaller than 3.0 mass %. In addition,from a viewpoint of improving the dispersibility of the ferromagnetichexagonal ferrite powder, the polyalkyleneimine chain percentage ispreferably equal to or greater than 0.2 mass %, more preferably equal toor greater than 0.3 mass %, and even more preferably equal to or greaterthan 0.5 mass %.

The percentage of the polyalkyleneimine chain described above can becontrolled, for example, according to a mixing ratio ofpolyalkyleneimine and polyester used at the time of synthesis.

The percentage of the polyalkyleneimine chain occupying thepolyalkyleneimine derivative can be calculated from an analysis resultobtained by element analysis such as nuclear magnetic resonance (NMR),more specifically, ¹H-NMR and ¹³C-NMR, and a well-known method. Thevalue calculated as described is the same as a theoretical valueacquired from a compounding ratio of a synthesis raw material in thepolyalkyleneimine derivative, and thus, the theoretical value acquiredfrom the compounding ratio can be used as the percentage of thepolyalkyleneimine chain occupying the polyalkyleneimine derivative.

Structure of Polyalkyleneimine Chain

The polyalkyleneimine chain has a polymer structure including the sameor two or more different alkyleneimine chains. As the alkyleneiminechain included, an alkyleneimine chain represented by the followingFormula A and an alkyleneimine chain represented by Formula B can beused. In the alkyleneimine chains represented by the following Formulae,the alkyleneimine chain represented by Formula A can include a bondingsite with a polyester chain. In addition, the alkyleneimine chainrepresented by Formula B can be bonded to a polyester chain by the saltcrosslinking agent described above. The polyalkyleneimine derivative canhave a structure in which one or more polyester chains are bonded to thepolyalkyleneimine chain, by including one or more alkyleneimine chains.In addition, the polyalkyleneimine chain may be formed of only a linearstructure or may have a branched tertiary amine structure. It ispreferable that the polyalkyleneimine chain has a branched structure,from a viewpoint of further improving the dispersibility. As a componenthaving a branched structure, a component bonded to an adjacentalkyleneimine chain at *¹ in the following Formula A and a componentbonded to an adjacent alkyleneimine chain at *² in the following FormulaB can be used.

In Formula A, R¹ and R² each independently represent a hydrogen atom oran alkyl group, a1 represents an integer equal to or greater than 2, and*¹ represents a bonding site with a polyester chain, an adjacentalkyleneimine chain, a hydrogen atom, or a substituent.

In Formula B, R³ and R⁴ each independently represent a hydrogen atom oran alkyl group, and a2 represents an integer equal to or greater than 2.The alkyleneimine chain represented by Formula B is bonded to apolyester chain including an anionic group by forming a saltcrosslinking group by N⁺ in Formula B and an anionic group included inthe polyester chain.

* in Formula A and Formula B and *² in Formula B each independentlyrepresent a site to be bonded to an adjacent alkyleneimine chain, ahydrogen atom, or a substituent.

Hereinafter, Formula A and Formula B will be further described indetail.

R¹ and R² in Formula A and R³ and R⁴ in Formula B each independentlyrepresent a hydrogen atom or an alkyl group. As the alkyl group, forexample, an alkyl group having 1 to 6 carbon atoms can be used, and thealkyl group is preferably an alkyl group having 1 to 3 carbon atoms,more preferably a methyl group or an ethyl group, and even morepreferably a methyl group. As an aspect of a combination of R¹ and R² inFormula A, an aspect in which one is a hydrogen atom and the other is analkyl group, an aspect in which both of them are hydrogen atoms, and anaspect in which both of them are alkyl groups (alkyl groups which arethe same as each other or different from each other) are used, and theaspect in which both of them are hydrogen atoms is preferably used. Thepoint described above is also applied to R³ and R⁴ in Formula B in thesame manner.

Ethyleneimine has a structure having the minimum number of carbon atomsconfiguring a ring as alkyleneimine, and the number of carbons of a mainchain of the alkyleneimine chain (ethyleneimine chain) obtained by ringopening of ethyleneimine is 2. Accordingly, the lower limit of a1 inFormula A and a2 in Formula B is 2. That is, a1 in Formula A and a2 inFormula B each independently represent an integer equal to or greaterthan 2. a1 in Formula A and a2 in Formula B are each independentlypreferably equal to or smaller than 10, more preferably equal to orsmaller than 6, even more preferably equal to or smaller than 4, stillmore preferably 2 or 3, and still even more preferably 2, from aviewpoint of adsorption properties to the surface of the particles ofthe ferromagnetic powder.

The details of the bonding between the alkyleneimine chain representedby Formula A or the alkyleneimine chain represented by Formula B and thepolyester chain are as described above.

Each alkyleneimine chain is bonded to an adjacent alkyleneimine chain, ahydrogen atom, or a substituent, at a position represented by * in eachFormula. As the substituent, for example, a monovalent substituent suchas an alkyl group (for example, an alkyl group having 1 to 6 carbonatoms) can be used, but there is no limitation. In addition, thepolyester chain may be bonded as the substituent.

Weight-Average Molecular Weight of Polyalkyleneimine Derivative Amolecular weight of the polyalkyleneimine derivative is preferably 1,000to 80,000 as the weight-average molecular weight as described above. Theweight-average molecular weight of the polyalkyleneimine derivative ismore preferably equal to or greater than 1,500, even more preferablyequal to or greater than 2,000, and further more preferably equal to orgreater than 3,000. In addition, the weight-average molecular weight ofthe polyalkyleneimine derivative is more preferably equal to or smallerthan 60,000, even more preferably equal to or smaller than 40,000, andfurther more preferably equal to or smaller than 35,000, and still morepreferably equal to or smaller than 34,000. For measurement conditionsof the weight-average molecular weight of the polyalkyleneiminederivative, a specific example which will be described later can bereferred to.

Synthesis Method

The synthesis method is not particularly limited, as long as thepolyalkyleneimine derivative includes the polyester chain and thepolyalkyleneimine chain having a number average molecular weight of 300to 3,000 at the ratio described above. As a preferred aspect of thesynthesis method, descriptions disclosed in paragraphs 0061 to 0069 ofJP2015-28830A can be referred to.

As a specific example of the polyalkyleneimine derivative, variouspolyalkyleneimine derivatives shown in Table 2 synthesized by usingpolyethyleneimine and polyester shown in Table 2 can be used. For thedetails of the synthesis reaction, descriptions disclosed in exampleswhich will be described later and/or examples of JP2015-28830A can bereferred to.

TABLE 2 Percentage of Polyalkyleneimine PolyethyleneiminePolyalkyleneimine chain Weight-average (polyethyleneimine) amount(polyethyleneimine chain) Acid value Amine value molecular derivativePolyethyleneimine* (g) (mass %) Polyester (mgKOH/g) (mgKOH/g) weight(J-1)  SP-018 5 4.8 (i-1) 22.2 28.6 15,000 (J-2)  SP-006 2.4 2.3 (i-2)35 17.4 7,000 (J-3)  SP-012 4.5 4.3 (i-3) 6.5 21.2 22,000 (J-4)  SP-0065 4.8 (i-4) 4.9 11.8 34,000 (J-5)  SP-003 5 4.8 (i-5) 10.1 15.2 19,000(J-6)  SP-018 1.2 1.2 (i-6) 68.5 22.4 8,000 (J-7)  SP-018 3 2.9 (i-7)39.9 16.8 13,000 (J-8)  SP-012 2.5 2.4 (i-8) 15.5 18.9 18,000 (J-9) SP-006 5 4.8 (i-9) 11.1 16.8 22,000 (J-10) SP-003 4 3.8 (i-10) 4.4 14.124,000 (J-11) SP-012 0.3 0.3 (i-10) 8.1 7.8 28,000 (J-12) SP-018 1 1(i-1) 28.8 6.7 15,000 (J-13) SP-012 5 4.8 (i-6) 61 28.2 4,000 (J-14)SP-006 2.4 2.3 (i-11) 30 17.4 6,000 (J-15) SP-006 2.4 2.3 (i-12) 42.818.1 6,300 (J-16) SP-006 2.4 2.3 (i-13) 43.7 17.9 5,900 (J-17) SP-0062.4 2.3 (i-14) 42.5 17.1 5,300 (J-18) SP-006 2.3 2.4 (i-15) 37.5 19.47,300 (J-19) SP-006 2.3 2.4 (i-16) 24.6 16 9,800 (J-20) SP-006 2.3 2.4(i-17) 27.5 26.1 9,300 (J-21) SP-006 2.3 2.4 (i-18) 31.7 8.9 8,900(J-22) SP-006 2.3 2.4 (i-19) 15.3 13.9 15,100 (J-23) SP-006 2.3 2.4(i-20) 38.1 22.4 7,580 (*Note) Polyethyleneimine shown in Table 2 is asdescribed below. SP-003 (Polyethyleneimine (manufactured by NipponShokubai Co., Ltd.) number average molecular weight of 300) SP-006(Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.) numberaverage molecular weight of 600) SP-012 (Polyethyleneimine (manufacturedby Nippon Shokubai Co., Ltd.) number average molecular weight of 1,200)SP-018 (Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.)number average molecular weight of 1,800)

The polyester shown in Table 2 is polyester synthesized by thering-opening polymerization of lactone by using lactone and anucleophilic reagent (carboxylic acid) shown in Table 3. For the detailsof the synthesis reaction, descriptions disclosed in examples which willbe described later and/or examples of JP2015-28830A can be referred to.

TABLE 3 Amount of Number average Number of carboxylic acidWeight-average molecular lactone repeating Polyester Carboxylic acid (g)Lactone molecular weight weight units (i-1) n-octanoic acid 12.6ε-caprolactone 9,000 7,500 20 (i-2) n-octanoic acid 16.8 ε-caprolactone7,000 5,800 15 (i-3) n-octanoic acid 3.3 L-lactide 22,000 18,000 60(i-4) Palmitic acid 4.5 ε-caprolactone 38,000 31,000 100 (i-5) Palmiticacid 12.8 δ-valerolactone 16,000 13,000 40 (i-6) Stearic acid 99.7ε-caprolactone 2,500 2,000  5 (i-7) Glycol acid 13.3 ε-caprolactone4,800 4,000 10 (i-8) 12-hydroxystearic acid 20 δ-valerolactone 33,00010,000 30 (i-9) 12-hydroxystearic acid 13.2 ε-caprolactone 17,000 14,00040 (i-10) 2-naphthoic acid 3.8 ε-caprolactone 27,000 22,500 80 (i-11)[2-(2-methoxyethoxy)ethoxy]acetic 15.6 ε-caprolactone 8,700 6,300 15acid (i-12) n-octanoic acid 16.8 Lactide 8,100 4,100 15 (i-13)n-octanoic acid 17.31 L-lactide 6,900 3,500 10 (L-lactide derived)ε-caprolactone 5 (ε-caprolactone derived) (i-14) n-octanoic acid 17.31L-lactide 6,200 3,200 5 (L-lactide derived) ε-caprolactone 10(ε-caprolactone derived) (i-15) Nonafluorovaleric acid 30.8ε-caprolactone 9,000 7,500 15 (i-16) Heptadecafluorononatioic acid 54.2ε-caprolactone 8,000 5,000 15 (i-17) 3,5,5-trimethylhexanoic acid 18.5ε-caprolactone 10,000 5,800 15 (i-18) 4-oxovaleric acid 13.6ε-caprolactone 7,400 4,100 15 (i-19) [2-(2-methoxyethoxy)ethoxy]acetic20.8 ε-caprolactone 15,300 11,500 30 acid (i-20) Benzoic acid 14-3ε-caprolactone 7,000 3,000 15

The acid value and amine value described above are determined by apotentiometric method (solvent: tetrahydrofuran/water=100/10 (volumeratio), titrant: 0.01 N (0.01 mol/l), sodium hydroxide aqueous solution(acid value), 0.01 N (0.01 mol/l) hydrochloric acid (amine value)).

The average molecular weight (number average molecular weight andweight-average molecular weight) is acquired by performing referencepolystyrene conversion of a value measured by GPC.

Specific examples of the measurement conditions of the average molecularweights of polyester, polyalkyleneimine, and a polyalkyleneiminederivative are respectively as described below.

Measurement Conditions of Average Molecular Weight of PolyesterMeasurement device: HLC-8220 GPC (manufactured by Tosoh Corporation)Column: TSK gel Super HZ2000/TSK gel Super HZ 4000/TSK gel Super HZ—H(manufactured by Tosoh Corporation)

Eluent: Tetrahydrofuran (THF)

Flow rate: 0.35 ml/min

Column temperature: 40° C.

Detector: differential refractometry (RI) detector

Measurement Conditions of Average Molecular Weight of Polyalkyleneimineand Average Molecular Weight of Polyalkyleneimine Derivative

Measurement device: HLC-8320 GPC (manufactured by Tosoh Corporation)

Column: three TSK gel Super AWM-H (manufactured by Tosoh Corporation)

Eluent: N-methyl-2-pyrrolidone (10 mmol/l of lithium bromide is added asan additive)

Flow rate: 0.35 ml/min

Column temperature: 40° C.

Detector: differential refractometry (RI) detector

The dispersing agent described above is mixed with ferromagnetichexagonal ferrite powder having an activation volume equal to or smallerthan 1,600 nm³, a binder, and a solvent, and thus, the magnetic layerforming composition can be prepared. In addition, the magnetic layer ofthe magnetic tape can include the dispersing agent, together with theferromagnetic hexagonal ferrite powder having an activation volume equalto or smaller than 1,600 nm³ and the binder. The dispersing agent may beused alone or in combination of two or more kinds having differentstructures. In a case of using two more kinds thereof in combination,the content thereof means the total content of the compounds used incombination. The point described above is also applied to the content ofvarious components disclosed in the specification.

The content of the dispersing agent is preferably 0.5 to 25.0 parts bymass with respect to 100.0 parts by mass of the ferromagnetic hexagonalferrite powder. The content of the dispersing agent is preferably equalto or greater than 0.5 parts by mass, more preferably equal to orgreater than 1.0 part by mass, even more preferably equal to or greaterthan 5.0 parts by mass, and still more preferably equal to or greaterthan 10.0 parts by mass, with respect to 100.0 parts by mass of theferromagnetic hexagonal ferrite powder, from viewpoints of improving thedispersibility of the ferromagnetic hexagonal ferrite powder and thedurability of the magnetic layer. Meanwhile, it is preferable toincrease the filling percentage of the ferromagnetic hexagonal ferritepowder of the magnetic layer, in order to improve recording density.From this point, it is preferable that the content of the componentsother than the ferromagnetic hexagonal ferrite powder is relatively low.From the viewpoints described above, the content of the dispersing agentis preferably equal to or smaller than 25.0 parts by mass, morepreferably equal to or smaller than 20.0 parts by mass, even morepreferably equal to or smaller than 18.0 parts by mass, and still morepreferably equal to or smaller than 15.0 parts by mass with respect to100.0 parts by mass of the ferromagnetic hexagonal ferrite powder.

Hereinabove, the preferred method for setting the cos θ to be 0.85 to1.00 has been described. Here, setting the cos θ to be 0.85 to 1.00 isan example of preferred means for setting the difference(l_(99.9)−l_(0.1)) to be equal to or smaller than 180 nm. A magnetictape in which the cos θ is smaller than 0.85 is included in the magnetictape according to one aspect of the invention, as long as it is amagnetic tape including a magnetic layer including ferromagnetichexagonal ferrite powder having an activation volume equal to or smallerthan 1,600 nm³ and a binder on a non-magnetic support, in which themagnetic layer includes a timing-based servo pattern, and the difference(l_(99.9)−l_(0.1)) is equal to or smaller than 180 nm.

Hereinafter, the magnetic tape will be further described in detail.

Magnetic Layer

Ferromagnetic Powder

The magnetic layer includes ferromagnetic powder and a binder. Theferromagnetic powder is ferromagnetic hexagonal ferrite powder having anactivation volume equal to or smaller than 1,600 nm³. The details of theactivation volume of the ferromagnetic hexagonal ferrite powder are asdescribed above. A percentage of the hexagonal ferrite particles havingthe aspect ratio and the length in the long axis direction describedabove in all of the hexagonal ferrite particles observed in the STEMimage, can be, for example, equal to or greater than 50%, as apercentage with respect to all of the hexagonal ferrite particlesobserved in the STEM image, based on the particle number. In addition,the percentage can be, for example, equal to or smaller than 95% and canexceed 95%. For other details of ferromagnetic hexagonal ferrite powder,for example, descriptions disclosed in paragraphs 0012 to 0030 ofJP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, andparagraphs 0013 to 0030 of JP2012-204726A can be referred to.

The content (filling percentage) of the ferromagnetic hexagonal ferritepowder of the magnetic layer is preferably in a range of 50 to 90 mass %and more preferably in a range of 60 to 90 mass %. The component otherthan the ferromagnetic hexagonal ferrite powder of the magnetic layer isat least a binder and arbitrarily one or more kinds of additives can beincluded. The high filling percentage of the ferromagnetic hexagonalferrite powder of the magnetic layer is preferable, from a viewpoint ofimproving recording density.

Binder

The magnetic tape includes the ferromagnetic hexagonal ferrite powderand the binder in the magnetic layer. The binder is one or more kinds ofresin. As the binder, a resin from a polyurethane resin, a polyesterresin, a polyamide resin, a vinyl chloride resin, an acrylic resinobtained by copolymerizing styrene, acrylonitrile, or methylmethacrylate, a cellulose resin such as nitrocellulose, an epoxy resin,a phenoxy resin, and a polyvinylalkylal resin such as polyvinyl acetalor polyvinyl butyral can be used alone or a plurality of resins can bemixed with each other to be used. Among these, a polyurethane resin, anacrylic resin, a cellulose resin, and a vinyl chloride resin arepreferable. These resins may be a homopolymer or a copolymer. Theseresins can be used as the binder even in the non-magnetic layer and/or aback coating layer which will be described later. For the binderdescribed above, description disclosed in paragraphs 0028 to 0031 ofJP2010-24113A can be referred to. In addition, the binder may be aradiation curable resin such as an electron beam-curable resin. For theradiation curable resin, descriptions disclosed in paragraphs 0044 and0045 of JP2011-48878A can be referred to.

In addition, a curable agent can be used together with a resin which canbe used as the binder. The curable agent is a compound including atleast one and preferably two or more cross-linking functional groups inone molecule. As the curable agent, polyisocyanate is suitable. For thedetails of polyisocyanate, descriptions disclosed in paragraphs 0124 and0125 of JP2011-216149A can be referred to. The amount of the curableagent used can be, for example, 0 to 80.0 parts by mass with respect to100.0 parts by mass of the binder, and is preferably 50.0 to 80.0 partsby mass, from a viewpoint of improvement of strength of each layer suchas the magnetic layer.

Additive

The magnetic layer includes the ferromagnetic powder and the binder, andmay include one or more kinds of additives, if necessary. As theadditives, the dispersing agent and the curable agent described aboveare used, for example. At least a part of the curable agent is includedin the magnetic layer in a state of being reacted (crosslinked) withother components such as the binder, by proceeding the curing reactionin the magnetic layer forming step. In addition, examples of theadditive which can be included in the magnetic layer include anon-magnetic filler, a lubricant, a dispersing agent, a dispersingassistant, an antibacterial agent, an antistatic agent, an antioxidant,and carbon black. The non-magnetic filler is identical to thenon-magnetic powder. As the non-magnetic filler, a non-magnetic filler(hereinafter, referred to as a “projection formation agent”) which canfunction as a projection formation agent which forms projectionssuitably protruded from the surface of the magnetic layer, and anon-magnetic filler (hereinafter, referred to as an “abrasive”) whichcan function as an abrasive can be used. The projection formation agentis a component which can contribute to the control of frictionproperties of the surface of the magnetic layer. It is preferable thatat least one of the projection formation agent and the abrasive isincluded in the magnetic layer of the magnetic tape, and it ispreferable that both of them are included. As the additives, a suitableamount of a commercially available product or an additive prepared by awell-known method can be used according to desired properties.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape maydirectly include a magnetic layer on a non-magnetic support, or mayinclude a non-magnetic layer including non-magnetic powder and a binderbetween the non-magnetic support and the magnetic layer. Thenon-magnetic powder used in the non-magnetic layer may be inorganicsubstances or organic substances. In addition, carbon black and the likecan be used.

Examples of the inorganic substances include metal, metal oxide, metalcarbonate, metal sulfate, metal nitride, metal carbide, and metalsulfide. The non-magnetic powder can be purchased as a commerciallyavailable product or can be manufactured by a well-known method. Fordetails thereof, descriptions disclosed in paragraphs 0146 to 0150 ofJP2011-216149A can be referred to. For carbon black which can be used inthe non-magnetic layer, descriptions disclosed in paragraphs 0040 and0041 of JP2010-24113 can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably in a range of 50 to 90 mass % and more preferably in a rangeof 60 to 90 mass %.

In regards to other details of a binder or additives of the non-magneticlayer, the well-known technology regarding the non-magnetic layer can beapplied. In addition, in regards to the type and the content of thebinder, and the type and the content of the additive, for example, thewell-known technology regarding the magnetic layer can be applied.

The non-magnetic layer of the invention and the specification alsoincludes a substantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Back Coating Layer

The magnetic tape can also include a back coating layer includingnon-magnetic powder and a binder on a side of the non-magnetic supportopposite to the side including the magnetic layer. The back coatinglayer preferably includes any one or both of carbon black and inorganicpowder. In regards to the binder included in the back coating layer andvarious additives which can be arbitrarily included in the back coatinglayer, a well-known technology regarding the treatment of the magneticlayer and/or the non-magnetic layer can be applied.

Non-Magnetic Support

Next, the non-magnetic support (hereinafter, also simply referred to asa “support”) will be described. As the non-magnetic support, well-knowncomponents such as polyethylene terephthalate, polyethylene naphthalate,polyamide, polyamide imide, aromatic polyamide subjected to biaxialstretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or heatingtreatment may be performed with respect to these supports in advance.

Thicknesses of Non-Magnetic Support and Each Layer A thickness of thenon-magnetic support is preferably 3.0 to 20.0 μm, more preferably 3.0to 10.0 μm, and even more preferably 3.0 to 6.0 μm.

A thickness of the magnetic layer is preferably equal to or smaller than100 nm, from a viewpoint of high-density recording which is required inrecent years. The thickness of the magnetic layer is more preferably ina range of 10 nm to 100 nm and even more preferably in a range of 20 to90 nm. The magnetic layer may be at least single layer, the magneticlayer may be separated into two or more layers having different magneticproperties, and a configuration of a well-known multilayered magneticlayer can be applied. A thickness of the magnetic layer in a case wherethe magnetic layer is separated into two or more layers is the totalthickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm andis preferably 0.1 to 1.0 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.9 μm and even more preferably 0.1 to 0.7 μm.

The thicknesses of various layers of the magnetic tape and thenon-magnetic support can be acquired by a well-known film thicknessmeasurement method. As an example, a cross section of the magnetic tapein a thickness direction is, for example, exposed by a well-known methodof ion beams or microtome, and the exposed cross section is observedwith a scan electron microscope. In the cross section observation,various thicknesses can be acquired as a thickness acquired at oneposition of the cross section in the thickness direction, or anarithmetical mean of thicknesses acquired at a plurality of positions oftwo or more positions, for example, two positions which are arbitrarilyextracted. In addition, the thickness of each layer may be acquired as adesigned thickness calculated according to the manufacturing conditions.

Measurement Method

Manufacturing of Magnetic Tape in Which Servo Pattern is Formed

Each composition for forming the magnetic layer, the non-magnetic layer,or the back coating layer normally includes a solvent, together withvarious components described above. As the solvent, various organicsolvents generally used for manufacturing a coating type magnetic tapecan be used. The steps of preparing a composition for forming each layergenerally include at least a kneading step, a dispersing step, and amixing step provided before and after these steps, if necessary. Eachstep may be divided into two or more stages. All of raw materials usedin the invention may be added at an initial stage or in a middle stageof each step. In addition, each raw material may be separately added intwo or more steps. In the preparation of the magnetic layer formingcomposition, it is preferable that the abrasive and the ferromagneticpowder are separately dispersed as described above. In order tomanufacture the magnetic tape, a well-known manufacturing technology canbe used. In the kneading step, an open kneader, a continuous kneader, apressure kneader, or a kneader having a strong kneading force such as anextruder is preferably used. The details of the kneading processes ofthese kneaders are disclosed in JP1989-106338A (JP-H01-106338A) andJP1989-79274A (JP-H01-79274A). In addition, in order to disperse eachlayer forming composition, glass beads and one or more kinds of otherdispersion beads can be used as the dispersion medium. As suchdispersion beads, zirconia beads, titania beads, and steel beads whichare dispersion beads having high specific gravity are preferable. Thesedispersion beads can be used by optimizing a particle diameter (beaddiameter) and a filling percentage. As a dispersing machine, awell-known dispersing machine can be used. As one of means for obtaininga magnetic tape having cos θ of 0.85 to 1.00, a technology ofreinforcing the dispersion conditions (for example, increasing thedispersion time, decreasing the diameter of the dispersion beads usedfor dispersion and/or increasing the filling percentage of thedispersion beads, using the dispersing agent, and the like) is alsopreferable. A preferred aspect regarding the reinforcing of thedispersion conditions is as described above. For other details of themanufacturing method of the magnetic tape, for example, descriptionsdisclosed in paragraphs 0051 to 0057 of JP2010-24113A can be referredto.

For the orientation process, a description disclosed in a paragraph 0052of JP2010-24113A can be referred to. As one of means for obtaining amagnetic tape having cos θ of 0.85 to 1.00, a vertical orientationprocess is preferably performed.

Formation of Servo Pattern

The magnetic tape includes a timing-based servo pattern in the magneticlayer. FIG. 1 shows a disposition example of a region (servo band) inwhich the timing-based servo pattern is formed and a region (data band)interposed between two servo bands. FIG. 2 shows a disposition exampleof the timing-based servo patterns. Specific examples of the shapes ofthe timing-based servo patterns are shown in FIGS. 2 to 4 and FIGS. 6 to8. Here, the disposition example and/or shape shown in each drawing ismerely an example, and the servo pattern, the servo bands, and the databands may be disposed as the shape and disposition according to a systemof the magnetic tape device (drive). In addition, for the shape and thedisposition of the timing-based servo pattern, a well-known technologysuch as disposition examples shown in FIG. 4, FIG. 5, FIG. 6, FIG. 9,FIG. 17, and FIG. 20 of U.S. Pat. No. 5,689,384A can be applied withoutany limitation, for example.

The servo pattern can be formed by magnetizing a specific region of themagnetic layer by a servo write head mounted on a servo writer. A regionto be magnetized by the servo write head (position where the servopattern is formed) is determined by standards. As the servo writer, acommercially available servo writer or a servo writer having awell-known configuration can be used. For the configuration of the servowriter, well-known technologies such as technologies disclosed inJP2011-175687A, U.S. Pat. No. 5,689,384A, and U.S. Pat. No. 6,542,325Bcan be referred to without any limitation.

The magnetic tape described above includes the magnetic layer includingthe ferromagnetic hexagonal ferrite powder having an activation volumeof 1,600 nm³, and it is possible to improve head positioning accuracy ofthe timing-based servo system.

Magnetic Tape Device

One aspect of the invention relates to a magnetic tape device includingthe magnetic tape, a magnetic head, and a servo head.

The details of the magnetic tape mounted on the magnetic tape device areas described above. Such a magnetic tape includes timing-based servopatterns. Accordingly, a magnetic signal is recorded on the data band bythe magnetic head to form a data track, and/or, when reproducing therecorded signal, a head tracking of a timing-based servo type isperformed based on the read servo pattern, while reading the servopattern by the servo head, and accordingly, it is possible to cause themagnetic head to follow the data track with high accuracy. As an indexof the head positioning accuracy, a position error signal (PES) acquiredby a method shown in examples which will be described later can be used.The PES is an index showing that the magnetic head runs a positiondeviated from a position where the magnetic head should run, even whenthe head tracking is performed by the servo system, when the magnetictape runs in the magnetic tape device. A high value means that thedeviation becomes great and the head positioning accuracy of the servosystem is low. In the magnetic tape according to one aspect of theinvention, for example, the PES equal to or smaller than 9.0 nm (forexample, range of 7.0 to 9.0 nm) can be achieved.

As the magnetic head mounted on the magnetic tape device, a well-knownmagnetic head which can perform the recording and/or reproducing of themagnetic signal with respect to the magnetic tape can be used. Arecording head and a reproduction head may be one magnetic head or maybe separated magnetic heads. As the servo head, a well-known servo headwhich can read the timing-based servo pattern of the magnetic tape canbe used. At least one or two or more servo heads may be included in themagnetic tape device.

For details of the head tracking of the timing-based servo system, forexample, well-known technologies such as technologies disclosed in U.S.Pat. No. 5,689,384A, U.S. Pat. No. 6,542,325B, and U.S. Pat. No.7,876,521B can be used without any limitation.

A commercially available magnetic tape device generally includes amagnetic head and a servo head in accordance to a standard. In addition,a commercially available magnetic tape device generally has a servocontrolling mechanism for realizing head tracking of the timing-basedservo system in accordance to a standard. The magnetic tape deviceaccording to one aspect of the invention can be configured byincorporating the magnetic tape according to one aspect of the inventionto a commercially available magnetic tape device.

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to aspects shown in the examples.“Parts” and “%” in the following description mean “parts by mass” and“mass %”, unless otherwise noted.

An average particle size described below is a value measured by a methoddisclosed in paragraphs 0058 to 0061 of JP2016-071926A. The measurementwas performed by using transmission electron microscope H-9000manufactured by Hitachi, Ltd. as the transmission electron microscope,and image analysis software KS-400 manufactured by Carl Zeiss as theimage analysis software.

Examples 1 to 7 and Comparative Examples 1 to 7

1. Preparation of Alumina Dispersion (Abrasive Liquid)

3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 31.3 parts of 32% solution (solvent is a mixedsolvent of methyl ethyl ketone and toluene) of a polyester polyurethaneresin having a SO₃Na group as a polar group (UR-4800 manufactured byToyobo Co., Ltd. (amount of a polar group: 80 meq/kg)), and 570.0 partsof a mixed liquid of methyl ethyl ketone and cyclohexanone at 1:1 (massratio) as a solvent were mixed with 100.0 parts of alumina powder(HIT-80 manufactured by Sumitomo Chemical Co., Ltd., Mohs hardness of 9)having an gelatinization ratio of approximately 65% andBrunauer-Emmett-Teller (BET) specific surface area of 20 m²/g, anddispersed in the presence of zirconia beads by a paint shaker for 5hours. After the dispersion, the dispersion liquid and the beads wereseparated by a mesh and an alumina dispersion (abrasive liquid) wasobtained.

2. Magnetic Layer Forming Composition List

Magnetic Solution

Ferromagnetic hexagonal ferrite powder (activation volume: see Table 4):100.0 parts

SO₃Na group-containing polyurethane resin: 14.0 parts

(Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g)

Dispersing agent: see Table 4

Cyclohexanone: 150.0 parts

Methyl ethyl ketone: 150.0 parts

Abrasive liquid

Alumina dispersion prepared in the section 1.0:6.0 parts

Silica Sol (Projection Formation Agent Liquid)

Colloidal silica (average particle size of 100 nm): 2.0 parts

Methyl ethyl ketone: 1.4 parts

Other Components

Stearic acid: 2.0 parts

Butyl stearate: 6.0 parts

Polyisocyanate (CORONATE (registered trademark) manufactured by NipponPolyurethane Industry): 2.5 parts

Finishing Additive Solvent

Cyclohexanone: 200.0 parts

Methyl ethyl ketone: 200.0 parts

The synthesis method or the like of the dispersing agent shown in Table4 will be described later in detail.

3. Non-Magnetic Layer Forming Composition List

Nonmagnetic inorganic powder: α-iron oxide: 100.0 parts

Average particle size (average long axis length): 0.15 μm

Average acicular ratio: 7

BET specific surface area: 52 m²/g

Carbon black: 20.0 parts

Average particle size: 20 nm

SO₃Na group-containing polyurethane resin: 18.0 parts

(Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g)

Stearic acid: 1.0 part

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

4. Back Coating Layer Forming Composition List

Nonmagnetic inorganic powder: α-iron oxide: 80.0 parts

Average particle size (average long axis length): 0.15 μm

Average acicular ratio: 7

BET specific surface area: 52 m²/g

Carbon black: 20.0 parts

Average particle size: 20 nm

Vinyl chloride copolymer: 13.0 parts

Sulfonate group-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Methyl ethyl ketone: 155.0 parts

Stearic acid: 3.0 parts

Butyl stearate: 3.0 parts

Polyisocyanate: 5.0 parts

Cyclohexanone: 355.0 parts

5. Preparation of Each Layer Forming Composition

(1) Preparation of Magnetic Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

A magnetic solution was prepared by performing beads dispersing of themagnetic solution components described above by using beads as thedispersion medium in a batch type vertical sand mill. Specifically, thedispersion process was performed for the dispersion retention time shownin Table 4 by using zirconia beads having a bead diameter shown in Table4, as the beads dispersion of each stage (first stage and second stage,or first to third stages). In the beads stage, dispersion liquidobtained by using filter (average hole diameter of 5 Lm) was filteredafter completion of each stage. In the beads dispersion of each stage,the filling percentage of the dispersion medium was set to beapproximately 50 to 80 volume %.

The magnetic solution obtained as described above was mixed with theabrasive liquid, silica sol, other components, and the finishingadditive solvent and beads-dispersed for 5 minutes by using the sandmill, and ultrasonic dispersion was performed with a batch typeultrasonic device (20 kHz, 300 W) for 0.5 minutes. After that, theobtained mixed liquid was filtered by using a filter (average holediameter of 0.5 μm), and the magnetic layer forming composition wasprepared.

A circumferential speed of a tip of the sand mill at the time of beadsdispersion was in a range of 7 to 15 m/sec.

(2) Preparation of Non-Magnetic Layer Forming Composition

The non-magnetic layer forming composition was prepared by the followingmethod.

Each component excluding stearic acid, cyclohexanone, and methyl ethylketone was beads-dispersed by using batch type vertical sand mill(dispersion medium: zirconia beads (beads diameter: 0.1 mm), dispersionretention time: 24 hours) to obtain dispersion liquid. After that, theremaining components were added into the obtained dispersion liquid andstirred with a dissolver. Then, the obtained dispersion liquid wasfiltered by using the filter (average hole diameter of 0.5 μm), and anon-magnetic layer forming composition was prepared.

(3) Preparation of Back Coating Layer Forming Composition

The back coating layer forming composition was prepared by the followingmethod.

Each component excluding stearic acid, butyl stearate, polyisocyanate,and cyclohexanone was kneaded and diluted by an open kneader. Then, theobtained mixed liquid was subjected to a dispersion process of 12passes, with a transverse beads mill by using zirconia beads having abead diameter of 1 mm, by setting a bead filling percentage as 80 volume%, a circumferential speed of rotor tip as 10 m/sec, and a retentiontime for 1 pass as 2 minutes. After that, the remaining components wereadded into the obtained dispersion liquid and stirred with a dissolver.Then, the obtained dispersion liquid was filtered with a filter (averagehole diameter of 1 μm) and a back coating layer forming composition wasprepared.

6. Manufacturing of Magnetic Tape and Formation of Timing-Based ServoPattern

The non-magnetic layer forming composition prepared in the section 5.(2)was applied onto a surface of a support made of polyethylene naphthalatehaving a thickness of 5.0 μm so that the thickness after the dryingbecomes 0.1 μm and was dried to form a non-magnetic layer. Then, themagnetic layer forming composition prepared in the section 5.(1) wasapplied onto a non-magnetic layer so that the thickness after the dryingbecomes 70 nm. In examples and comparative examples in which “performed”was shown in the column of the vertical orientation process in Table 4,the vertical orientation process was performed by applying a magneticfield having a magnetic field strength of 0.3 T to the surface of thecoating layer in a vertical direction, while the coated magnetic layerforming composition was dried, and then, the drying was performed, toform a magnetic layer. In comparative examples in which “not performed”was shown in the column of the vertical orientation process in Table 4,the coated magnetic layer forming composition was dried withoutperforming the vertical orientation process, and a magnetic layer wasformed.

After that, the back coating layer forming composition prepared in thesection 5.(3) was applied to the surface of the support made ofpolyethylene naphthalate on a side opposite to the surface where thenon-magnetic layer and the magnetic layer are formed, so that thethickness after the drying becomes 0.4 μm, and drying was performed toobtain a laminate.

Then, a surface smoothing treatment (calender process) was performedwith respect to the obtained laminate with a calender configured of onlya metal roll, at a calender process speed of 100 m/min, linear pressureof 294 kN/m (300 kg/cm), and a surface temperature of a calendering rollof 100°. After that, a heating process was performed in the environmentof the atmosphere temperature of 70° C. for 36 hours. The laminatesubjected to the heating process was cut to have a width of ½ inches(0.0127 meters) by using a slitter, and a magnetic tape wasmanufactured.

In a state where the magnetic layer of the manufactured magnetic tapewas demagnetized, servo patterns having dispositions and shapesaccording to the LTO Ultrium format were formed on the magnetic layer byusing a servo write head mounted on a servo writer. Accordingly, eachmagnetic tape of Examples and Comparative Examples including data bands,servo bands, and guide bands in the disposition according to the LTOUltrium format in the magnetic layer, and including servo patternshaving the disposition and the shape according to the LTO Ultrium formaton the servo band was obtained.

It can be said that the servo write head used for forming the servopattern has high capability of recording the servo pattern, as the valueof leakage field is great. In Examples and Comparative Examples, two ormore servo write heads having different leakage fields were used. Theleakage fields are shown in Table 4.

7. Preparation of Dispersing Agent

Dispersing agents 1 to 4 shown in Table 4 were prepared by the followingmethod. Hereinafter, a temperature shown regarding the synthesisreaction is a temperature of a reaction liquid.

In Comparative Example 7, 2,3-dihydroxynaphthalene was used instead ofthe dispersing agents 1 to 4. 2,3-dihydroxynaphthalene is a compoundused as an additive for adjusting a squareness ratio in JP2012-203955A.

(1) Preparation of Dispersing Agent 1

Synthesis of Precursor 1

197.2 g of ε-caprolactone and 15.0 g of 2-ethyl-1-hexanol wereintroduced into a 500 mL three-neck flask and stirred and decomposedwhile blowing nitrogen. 0.1 g of monobutyltin oxide was added theretoand heated to 100° C. After 8 hours, the elimination of the raw materialwas confirmed by gas chromatography, the resultant material was cooledto room temperature, and 200 g of a solid precursor 1 (followingstructure) was obtained.

Synthesis of Dispersing Agent 1

40.0 g of the obtained precursor 1 was introduced into 200 mL three-neckflask, and stirred and decomposed at 80° C. while blowing nitrogen. 2.2g of meso-butane-1,2,3,4-tetracarboxylic dianhydride was added theretoand heated to 110° C. After 5 hours, the elimination of a peak derivedfrom the precursor 1 was confirmed by ¹H-NMR, and then, the resultantmaterial was cooled to room temperature, and 38 g of a solid reactionproduct 1 (mixture of the following structural isomer) was obtained. Thereaction product 1 obtained as described above is a mixture of thecompound 1 shown in Table 1 and the structural isomer. The reactionproduct 1 is called a “dispersing agent 1”.

(2) Preparation of Dispersing Agent 2

Synthesis of Dispersing Agent 2

The synthesis was performed in the same manner as in the synthesis ofthe dispersing agent 1, except for changing 2.2 g ofbutanetetracarboxylic acid anhydride and 2.4 g of pyromellitic aciddianhydride, and 38 g of a solid reaction product 2 (mixture of thefollowing structural isomer) was obtained. The reaction product 2obtained as described above is a mixture of the compound 2 shown inTable 1 and the structural isomer. The reaction product 2 is called a“dispersing agent 2”.

(3) Preparation of Dispersing Agent 3

Synthesis of Polyester (i-1)

12.6 g of n-octanoic acid (manufactured by Wako Pure ChemicalIndustries, Ltd.) as carboxylic acid, 100 g of ε-caprolactone (PLACCEL Mmanufactured by Daicel Corporation) as lactone, and 2.2 g of monobutyltin oxide (manufactured by Wako Pure Chemical Industries, Ltd.)(C₄H₉Sn(O)OH) were mixed with each other in a 500 mL three-neck flask,and heated at 160° C. for 1 hour. 100 g of ε-caprolactone was addeddropwise for 5 hours, and further stirred for 2 hours. After that, thecooling was performed to room temperature, and polyester (i-1) wasobtained.

The synthesis scheme will be described below.

Synthesis of Dispersing Agent 3 (Polyethyleneimine Derivative (J-1))

5.0 g of polyethyleneimine (SP-018 manufactured by Nippon Shokubai Co.,Ltd., number average molecular weight of 1,800) and 100 g of theobtained polyester (i-1) were mixed with each other and heated at 110°C. for 3 hours, to obtain a polyethyleneimine derivative (J-1). Thepolyethyleneimine derivative (J-1) is called a “dispersing agent 3”.

The synthesis scheme is shown below. In the following synthesis scheme,a, b, c respectively represent a polymerization molar ratio of therepeating unit and is 0 to 50, and a relationship of a+b+c=100 issatisfied. 1, m, n1, and n2 respectively represent a polymerizationmolar ratio of the repeating unit, 1 is 10 to 90, m is 0 to 80, n1 andn2 are 0 to 70, and a relationship of 1+m+n1+n2=100 is satisfied.

(4) Preparation of Dispersing Agent 4

Synthesis of Polyester (i-2)

Polyester (i-2) was obtained in the same manner as in the synthesis ofthe polyester (i-1), except for changing the amount of carboxylic acidshown in Table 3.

Synthesis of Dispersing Agent 4 (Polyethyleneimine Derivative (J-2))

A polyethyleneimine derivative (J-2) was obtained by performing thesynthesis which is the same as that of the compound J-1, except forusing polyethyleneimine shown in Table 2 and the obtained polyester(i-2). The polyethyleneimine derivative (J-2) is called a “dispersingagent 4”.

The weight-average molecular weight of the dispersing agents 1 and 2 wasmeasured by a method described above as the measurement method of theweight-average molecular weight of the compound represented by GeneralFormula 1. As a result of the measurement, the weight-average molecularweight of the dispersing agent 1 was 9,200 and the weight-averagemolecular weight of the dispersing agent 2 was 6,300.

The weight-average molecular weight of the dispersing agent 3(polyethyleneimine derivative (J-1)) and the dispersing agent 4(polyethyleneimine derivative (J-2)) was a value shown in Table 3, whenthe value was acquired by performing reference polystyrene conversion ofa value measured by GPC under the measurement conditions of the specificexample described above.

The weight-average molecular weight other than that described above is avalue acquired by performing reference polystyrene conversion of a valuemeasured by GPC under the following measurement conditions.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mm (internal diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

8. Measurement of Activation Volume

The powder in a powder lot which is the same as that of ferromagnetichexagonal barium ferrite powder used in the preparation of the magneticlayer forming composition was used as a measurement sample of theactivation volume. The magnetic field sweep rates of the He measurementpart at time points of 3 minutes and 30 minutes were measured by usingan oscillation sample type magnetic-flux meter (manufactured by ToeiIndustry Co., Ltd.), and the activation volume was calculated from therelational expression described above. The measurement was performed inthe environment of 23° C.±1° C. The calculated activation volume isshown in Table 4.

9. Measurement of Cos θ

A cross section observation sample was cut out from each magnetic tapeof Examples and Comparative Examples, and cos θ described above wasacquired by using this sample by the method described above. In eachmagnetic tape of Examples and Comparative Examples, acquired cos θ isshown in Table 4. In each magnetic tape of Examples and ComparativeExamples, a percentage of hexagonal ferrite particles having the aspectratio and the length in the long axis direction of the ranges describedabove which is a measurement target of cos θ occupying all of thehexagonal ferrite particles observed in the STEM image, wasapproximately 80% to 95% based on the particle number.

The cross section observation sample used for the measurement of cos θwas manufactured by the following method.

(i) Manufacturing of Sample Including Protective Film

A sample including a protective film (laminated film of a carbon filmand a platinum film) was manufactured by the following method.

A sample having a size of a width direction 10 mm×longitudinal direction10 mm of the magnetic tape was cut out from the magnetic tape which is atarget acquiring the cos θ, with a blade. The width direction of thesample described below is a direction which was a width direction of themagnetic tape before the cutting out. The same applies to thelongitudinal direction.

A protective film was formed on the surface of the magnetic layer of thecut-out sample to obtain a sample including a protective film. Theformation of the protective film was performed by the following method.

A carbon film (thickness of 80 nm) was formed on the surface of themagnetic layer of the sample by vapor deposition, and a platinum (Pt)film (thickness of 30 nm) was formed on the surface of the formed carbonfilm by sputtering. The vapor deposition of the carbon film and thesputtering of the platinum film were respectively performed under thefollowing conditions.

Vapor Deposition Conditions of Carbon Film

Deposition source: carbon (core of a mechanical pencil having a diameterof 0.5 mm)

Degree of vacuum in a chamber of a vapor deposition device: equal to orsmaller than 2×10⁻³ Pa

Current value: 16 A

Sputtering Conditions of Platinum Film

Target: Pt

Degree of vacuum in a chamber of a sputtering device: equal to orsmaller than 7 Pa

Current value: 15 mA

(ii) Manufacturing Cross Section Observation Sample

A sample having a thin film shape was cut out from the sample includinga protective film manufactured in the section (i), by FIB processingusing a gallium ion (Ga) beam. The cutting out was performed byperforming the following FIB processing two times. An accelerationvoltage of the FIB processing was 30 kV.

In a first FIB processing, one end portion (that is, portion includingone side surface of the sample including a protective film in the widthdirection) of the sample including a protective film om the longitudinaldirection, including the area from the surface of the protective film toa region of a depth of approximately 5 μm was cut. The cut-out sampleincludes the area from the protective film to a part of the non-magneticsupport.

Then, a microprobe was loaded on a cut-out surface side (that is, samplecross section side exposed by the cutting out) of the cut-out sample andthe second FIB processing was performed. In the second FIB processing,the surface side opposite to the cut-out surface side (that is, one sidesurface in the width direction) was irradiated with a gallium ion beamto perform the cutting out of the sample. The sample was fixed bybonding the cut-out surface of the second FIB processing to the endsurface of the mesh for STEM observation. After the fixation, themicroprobe was removed.

In addition, the surface of the sample fixed to the mesh, from which themicroprobe is removed, was irradiated with a gallium ion beam at thesame acceleration voltage described above, to perform the FIBprocessing, and the sample fixed to the mesh was further thinned.

The cross section observation sample fixed to the mesh described asdescribed above was observed by a scanning transmission electronmicroscope, and the cos θ was acquired by the method described above.The cos θ acquired as described above is shown in Table 4.

10. Evaluation of Squareness Ratio (SQ)

The squareness ratio of each magnetic tape manufactured was measured ata magnetic field strength of 1194 kA/m (15 kOe) by using a variationsample type fluxmeter. The measurement results are shown in Table 4.

11. Measurement and Calculation of Difference (l_(99.9)−l_(0.1))

In each magnetic tape of Examples and Comparative Examples, thedifference (l_(99.9)−l_(0.1)) was acquired by the following method.

The servo pattern (magnetized region) was extracted by performing therough measurement regarding the measurement range of 90 μm×90 μm of thesurface of the magnetic layer of the magnetic tape on which the servopattern is formed, at a pitch of 100 nm, by using Dimension 3100manufactured by Bruker in a frequency modulation mode as a magneticforce microscope, and by using SSS-MFMR (nominal radius of curvature of15 nm) manufactured by Nanoworld. A distance between the surface of themagnetic layer and a tip of the probe at the time of the magnetic forcemicroscope observation was equal to or smaller than 20 nm. Themeasurement range includes 5 servo patterns of the A burst formedaccording to the LTO Ultrium format, and thus, these 5 servo patternswere extracted.

A magnetic profile was obtained by performing the measurement regardingthe vicinity of the boundary between the magnetized region andnon-magnetized region of the edge of each servo pattern on a downstreamside with respect to the running direction, at a pitch of 5 nm by usingthe magnetic force microscope and the probe. The obtained magneticprofile is tilted by an angle α=12°, and thus, rotation correction wasperformed so as to satisfy the angle α=0° by the analysis software.

The measurement was performed at three different portions on the surfaceof the magnetic layer. Each measurement range included 5 servo patternsof the A burst.

After that, the difference (l_(99.9)−l_(0.1)) was acquired by the methoddescribed above by using the analysis software. As the analysissoftware, MATLAB manufactured by MathWorks can be used. The difference(l_(99.9)−l_(0.1)) acquired as described above is shown in Table 4.

12. Measurement of PES

Regarding each magnetic tape of Examples and Comparative Examples, theservo pattern was read by a verify head on the servo writer using theformation of the servo pattern. The verify head is a reading magnetichead for confirming quality of the servo pattern formed in the magnetictape, an element for reading is disposed at a position corresponding tothe position of the servo pattern (position of the magnetic tape in thewidth direction), in the same manner as the magnetic head of thewell-known magnetic tape device (drive).

A well-known PES operation circuit which calculates the head positioningaccuracy of the servo system as PES from an electric signal obtained byreading the servo pattern by the verify head is connected to the verifyhead. The PES operation circuit calculates displacement of the inputelectric signal (pulse signal) in a width direction of the magnetictape, and calculates a value obtained by applying a highpass filter (cutoff value: 500 cycles/m) with respect to time variation information(signal) of this displacement, as PES. The calculated PES is shown inTable 4.

TABLE 4 Magnetic solution beads dispersion conditions FerromagneticFirst stage Second stage hexagonal ferrite Dispersion Dispersion powderDispersing agent retention Beads retention Beads activation volumeContent time diameter time diameter [nm³] Type [part] [h] [mm] [h] [mm]Comparative 2500 — — 10 0.5 — — Example 1 Comparative 2000 — — 10 0.5 —— Example 2 Comparative 1800 — — 10 0.5 — — Example 3 Comparative 1600 —— 10 0.5 — — Example 4 Comparative 1300 — — 10 0.5 — — Example 5Comparative 1600 — — 10 0.5 — — Example 6 Comparative 16002,3-dihydroxynaphthalene 12.0 10 0.5 10 0.1 Example 7 Example 1 1600Dispersion liquid 1 6.0 10 0.5 10 0.1 Example 2 1600 Dispersion liquid 112.0 10 0.5 30 0.1 Example 3 1600 Dispersion liquid 1 12.0 10 0.5 10 0.1Example 4 1600 Dispersion liquid 2 6.0 10 0.5 10 0.1 Example 5 1600Dispersion liquid 3 6.0 10 0.5 10 0.1 Example 6 1600 Dispersion liquid 46.0 10 0.5 10 0.1 Example 7 1300 Dispersion liquid 1 12.0 10 0.5 10 0.1Magnetic solution beads dispersion conditions Servo Evaluation resultThird stage write Servo Dispersion head pattern retention Beads VerticalLeakage difference time diameter orientation field SQ Cos θ(I_(99.9)-I_(0.1)) PES [h] [mm] process [kA/m] [—] [—] [nm] [nm]Comparative — — Not 247 0.58 0.68 158 8.5 Example 1 performedComparative — — Not 247 0.58 0.68 163 8.5 Example 2 performedComparative — — Not 247 0.55 0.68 162 8.6 Example 3 performedComparative — — Not 247 0.54 0.65 242 13.1 Example 4 performedComparative — — Not 247 0.54 0.65 288 14.5 Example 5 performedComparative — — Not 366 0.54 0.65 229 11.7 Example 6 performedComparative — — Performed 247 0.78 0.80 207 11.3 Example 7 Example 1 — —Performed 247 0.73 0.87 142 8.6 Example 2 — — Performed 247 0.74 0.96 888.1 Example 3 10 0.05 Performed 247 0.74 0.98 80 8.0 Example 4 — —Performed 247 0.73 0.87 128 8.4 Example 5 — — Performed 247 0.73 0.85175 8.7 Example 6 — — Performed 247 0.73 0.85 172 8.6 Example 7 10 0.05Performed 247 0.73 0.95 92 8.2

The PES acquired by the method described above which is equal to orsmaller than 9.0 nm means that it is possible to position the recordinghead with a high accuracy by head tracking of the timing-based servosystem.

When Comparative Examples 1 to 3 and Comparative Examples 4 to 7 arecompared to each other, it can be confirmed that a phenomenon in whichthe PES greatly exceeds 9.0 nm, that is, a decrease in head positioningaccuracy occurs in the magnetic tape (Comparative Examples 4 to 7) inwhich an activation volume of the ferromagnetic hexagonal ferrite powderincluded in the magnetic layer is equal to or smaller than 1,600 nm³. Inaddition, it can be also confirmed that it is difficult to prevent adecrease in head positioning accuracy by improving recording performanceof the servo write head (see Comparative Example 6).

With respect to this, in the magnetic tapes of Examples 1 to 7, althoughthe difference (l_(99.9)−l_(0.1)) is equal to or smaller than 180 nm andthe activation volume of the ferromagnetic hexagonal ferrite powderincluded in the magnetic layer is equal to or smaller than 1,600 nm³,the PES can be equal to or smaller than 9.0 nm. That is, in the magnetictape of Examples 1 to 7, it was possible to improve the head positioningaccuracy of the timing-based servo system.

In addition, from the result shown in Table 4, it can be confirmed thatthe cos θ, the difference (l_(99.9)−l_(0.1)), and the PES satisfy anexcellent correlation in which, when the cos θ increases, the difference(l_(99.9)−l_(0.1)) is decreased and the PES is decreased. With respectto this, such a correlation was not observed between the squareness(SQ), the difference (l_(99.9)−l_(0.1)), and the PES as shown in Table4.

An aspect of the invention can be effective in technical fields ofmagnetic tapes for high-density recording.

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; a magnetic layer including ferromagnetic powder and a binderformed on the non-magnetic support, wherein the magnetic layer includesa timing-based servo pattern, the ferromagnetic powder is ferromagnetichexagonal ferrite powder having an activation volume equal to or smallerthan 1,600 nm³, and an edge shape of the timing-based servo patternspecified by a magnetic force microscope observation is a shape in whicha difference, l_(99.9)−l_(0.1), between a value l_(99.9) of a cumulativefrequency function of 99.9% of a position deviation width from an idealshape in a longitudinal direction of the magnetic tape and a valuel_(0.1) of the cumulative frequency function of 0.1% is equal to orsmaller than 180 nm.
 2. The magnetic tape according to claim 1, whereinthe timing-pattern servo pattern is a linear servo pattern whichcontinuously or discontinuously extends from one side to the other sidein the width direction of the magnetic tape.
 3. The magnetic tapeaccording to claim 2, wherein the timing-based servo pattern is a linearservo pattern which continuously extends from one side to the other sidein a width direction of the magnetic tape and is tilted by an angle αwith respect to the width direction, and has the ideal shape which is alinear shape extending in a direction of the angle α.
 4. The magnetictape according to claim 1, wherein a tilt cos θ of the ferromagnetichexagonal ferrite powder with respect to a surface of the magnetic layeracquired by cross section observation performed by using a scanningtransmission electron microscope is 0.85 to 1.00.
 5. The magnetic tapeaccording to claim 4, wherein the cos θ is 0.89 to 1.00.
 6. The magnetictape according to claim 2, wherein a tilt cos θ of the ferromagnetichexagonal ferrite powder with respect to a surface of the magnetic layeracquired by cross section observation performed by using a scanningtransmission electron microscope is 0.85 to 1.00.
 7. The magnetic tapeaccording to claim 6, wherein the cos θ is 0.89 to 1.00.
 8. The magnetictape according to claim 3, wherein a tilt cos θ of the ferromagnetichexagonal ferrite powder with respect to a surface of the magnetic layeracquired by cross section observation performed by using a scanningtransmission electron microscope is 0.85 to 1.00.
 9. The magnetic tapeaccording to claim 8, wherein the cos θ is 0.89 to 1.00.
 10. Themagnetic tape according to claim 1, the magnetic layer further includesa polyester chain-containing compound having a weight-average molecularweight of 1,000 to 80,000.
 11. The magnetic tape according to claim 1,wherein the difference, l_(99.9)−l_(0.1), is equal to or smaller than100 nm.
 12. The magnetic tape according to claim 1, wherein anactivation volume of the ferromagnetic hexagonal ferrite powder is 800nm³ to 1,600 nm³.
 13. The magnetic tape according to claim 1, furthercomprising: a non-magnetic layer including non-magnetic powder and abinder, between the non-magnetic support and the magnetic layer.
 14. Amagnetic tape device comprising: a magnetic tape; a magnetic head; and aservo head, wherein the magnetic tape is a magnetic tape comprising: anon-magnetic support; a magnetic layer including ferromagnetic powderand a binder formed on the non-magnetic support, wherein the magneticlayer includes a timing-based servo pattern, the ferromagnetic powder isferromagnetic hexagonal ferrite powder having an activation volume equalto or smaller than 1,600 nm³, and an edge shape of the timing-basedservo pattern specified by a magnetic force microscope observation is ashape in which a difference, l_(99.9)−l_(0.1), between a value l_(99.9)of a cumulative frequency function of 99.9% of a position deviationwidth from an ideal shape in a longitudinal direction of the magnetictape and a value l_(0.1) of the cumulative frequency function of 0.1% isequal to or smaller than 180 nm.
 15. The magnetic tape device accordingto claim 14, wherein the timing-pattern servo pattern is a linear servopattern which continuously or discontinuously extends from one side tothe other side in the width direction of the magnetic tape.
 16. Themagnetic tape device according to claim 15, wherein the timing-basedservo pattern is a linear servo pattern which continuously extends fromone side to the other side in a width direction of the magnetic tape andis tilted by an angle α with respect to the width direction, and has theideal shape which is a linear shape extending in a direction of theangle α.
 17. The magnetic tape device according to claim 14, wherein atilt cos θ of the ferromagnetic hexagonal ferrite powder with respect toa surface of the magnetic layer acquired by cross section observationperformed by using a scanning transmission electron microscope is 0.85to 1.00.
 18. The magnetic tape device according to claim 17, wherein thecos θ is 0.89 to 1.00.